Export of internal Abseil changes

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3dbb096e4662311f81df1017a8e0975e903936cf by Derek Mauro <dmauro@google.com>:

Document and workaround a known MSVC bug doing constexpr pointer arithmetic

PiperOrigin-RevId: 262604652

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b5fa7f1a0c776f6ba20d52772a1679ec42ad21fd by Derek Mauro <dmauro@google.com>:

Fix typo in macos_xcode_bazel.sh

PiperOrigin-RevId: 262591285

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89dd77ab5bb44d76b6cb6b2f288e21536e16a85a by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 262582747

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32295ed9a0c6c8ab143a912194040eede05d3ea3 by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 262569140

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7f0f5b94197369228024529022d727439d2c894f by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 262563554

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314aed043639abbd221074125c57b7c68616de7e by Derek Mauro <dmauro@google.com>:

Release absl::btree

PiperOrigin-RevId: 262553526

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72b44056c6ce9000c4a6cd9aec58b82067c82a13 by CJ Johnson <johnsoncj@google.com>:

Internal change

PiperOrigin-RevId: 262421185

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4e2c12151edf534f929e8e810f1334073f90489a by Abseil Team <absl-team@google.com>:

Update documentation to make it less likely for users to write `Hours(24)` without considering using civil dates instead.

PiperOrigin-RevId: 262420758

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92b85b9573e800bd96b019408eefbc5ce4f68780 by Derek Mauro <dmauro@google.com>:

Add the ability to override the bazel version in the macos_xcode_bazel.sh
test script.

PiperOrigin-RevId: 262412063
GitOrigin-RevId: 3dbb096e4662311f81df1017a8e0975e903936cf
Change-Id: I423b2b829dc0c5f814e37bec4d68c7470f43f041

1 files changed, 2243 insertions, 0 deletions

diff --git a/absl/container/btree_test.cc b/absl/container/btree_test.cc
new file mode 100644
index 000000000000..a330cca32b90
--- /dev/null
+++ b/absl/container/btree_test.cc
@@ -0,0 +1,2243 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/container/btree_test.h"
+
+#include <cstdint>
+#include <map>
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/container/btree_map.h"
+#include "absl/container/btree_set.h"
+#include "absl/container/internal/counting_allocator.h"
+#include "absl/container/internal/test_instance_tracker.h"
+#include "absl/flags/flag.h"
+#include "absl/hash/hash_testing.h"
+#include "absl/memory/memory.h"
+#include "absl/meta/type_traits.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/str_split.h"
+#include "absl/strings/string_view.h"
+#include "absl/types/compare.h"
+
+ABSL_FLAG(int, test_values, 10000, "The number of values to use for tests");
+
+namespace absl {
+namespace container_internal {
+namespace {
+
+using ::absl::test_internal::InstanceTracker;
+using ::absl::test_internal::MovableOnlyInstance;
+using ::testing::ElementsAre;
+using ::testing::ElementsAreArray;
+using ::testing::IsEmpty;
+using ::testing::Pair;
+
+template <typename T, typename U>
+void CheckPairEquals(const T &x, const U &y) {
+  ABSL_INTERNAL_CHECK(x == y, "Values are unequal.");
+}
+
+template <typename T, typename U, typename V, typename W>
+void CheckPairEquals(const std::pair<T, U> &x, const std::pair<V, W> &y) {
+  CheckPairEquals(x.first, y.first);
+  CheckPairEquals(x.second, y.second);
+}
+}  // namespace
+
+// The base class for a sorted associative container checker. TreeType is the
+// container type to check and CheckerType is the container type to check
+// against. TreeType is expected to be btree_{set,map,multiset,multimap} and
+// CheckerType is expected to be {set,map,multiset,multimap}.
+template <typename TreeType, typename CheckerType>
+class base_checker {
+ public:
+  using key_type = typename TreeType::key_type;
+  using value_type = typename TreeType::value_type;
+  using key_compare = typename TreeType::key_compare;
+  using pointer = typename TreeType::pointer;
+  using const_pointer = typename TreeType::const_pointer;
+  using reference = typename TreeType::reference;
+  using const_reference = typename TreeType::const_reference;
+  using size_type = typename TreeType::size_type;
+  using difference_type = typename TreeType::difference_type;
+  using iterator = typename TreeType::iterator;
+  using const_iterator = typename TreeType::const_iterator;
+  using reverse_iterator = typename TreeType::reverse_iterator;
+  using const_reverse_iterator = typename TreeType::const_reverse_iterator;
+
+ public:
+  base_checker() : const_tree_(tree_) {}
+  base_checker(const base_checker &x)
+      : tree_(x.tree_), const_tree_(tree_), checker_(x.checker_) {}
+  template <typename InputIterator>
+  base_checker(InputIterator b, InputIterator e)
+      : tree_(b, e), const_tree_(tree_), checker_(b, e) {}
+
+  iterator begin() { return tree_.begin(); }
+  const_iterator begin() const { return tree_.begin(); }
+  iterator end() { return tree_.end(); }
+  const_iterator end() const { return tree_.end(); }
+  reverse_iterator rbegin() { return tree_.rbegin(); }
+  const_reverse_iterator rbegin() const { return tree_.rbegin(); }
+  reverse_iterator rend() { return tree_.rend(); }
+  const_reverse_iterator rend() const { return tree_.rend(); }
+
+  template <typename IterType, typename CheckerIterType>
+  IterType iter_check(IterType tree_iter, CheckerIterType checker_iter) const {
+    if (tree_iter == tree_.end()) {
+      ABSL_INTERNAL_CHECK(checker_iter == checker_.end(),
+                          "Checker iterator not at end.");
+    } else {
+      CheckPairEquals(*tree_iter, *checker_iter);
+    }
+    return tree_iter;
+  }
+  template <typename IterType, typename CheckerIterType>
+  IterType riter_check(IterType tree_iter, CheckerIterType checker_iter) const {
+    if (tree_iter == tree_.rend()) {
+      ABSL_INTERNAL_CHECK(checker_iter == checker_.rend(),
+                          "Checker iterator not at rend.");
+    } else {
+      CheckPairEquals(*tree_iter, *checker_iter);
+    }
+    return tree_iter;
+  }
+  void value_check(const value_type &x) {
+    typename KeyOfValue<typename TreeType::key_type,
+                        typename TreeType::value_type>::type key_of_value;
+    const key_type &key = key_of_value(x);
+    CheckPairEquals(*find(key), x);
+    lower_bound(key);
+    upper_bound(key);
+    equal_range(key);
+    contains(key);
+    count(key);
+  }
+  void erase_check(const key_type &key) {
+    EXPECT_FALSE(tree_.contains(key));
+    EXPECT_EQ(tree_.find(key), const_tree_.end());
+    EXPECT_FALSE(const_tree_.contains(key));
+    EXPECT_EQ(const_tree_.find(key), tree_.end());
+    EXPECT_EQ(tree_.equal_range(key).first,
+              const_tree_.equal_range(key).second);
+  }
+
+  iterator lower_bound(const key_type &key) {
+    return iter_check(tree_.lower_bound(key), checker_.lower_bound(key));
+  }
+  const_iterator lower_bound(const key_type &key) const {
+    return iter_check(tree_.lower_bound(key), checker_.lower_bound(key));
+  }
+  iterator upper_bound(const key_type &key) {
+    return iter_check(tree_.upper_bound(key), checker_.upper_bound(key));
+  }
+  const_iterator upper_bound(const key_type &key) const {
+    return iter_check(tree_.upper_bound(key), checker_.upper_bound(key));
+  }
+  std::pair<iterator, iterator> equal_range(const key_type &key) {
+    std::pair<typename CheckerType::iterator, typename CheckerType::iterator>
+        checker_res = checker_.equal_range(key);
+    std::pair<iterator, iterator> tree_res = tree_.equal_range(key);
+    iter_check(tree_res.first, checker_res.first);
+    iter_check(tree_res.second, checker_res.second);
+    return tree_res;
+  }
+  std::pair<const_iterator, const_iterator> equal_range(
+      const key_type &key) const {
+    std::pair<typename CheckerType::const_iterator,
+              typename CheckerType::const_iterator>
+        checker_res = checker_.equal_range(key);
+    std::pair<const_iterator, const_iterator> tree_res = tree_.equal_range(key);
+    iter_check(tree_res.first, checker_res.first);
+    iter_check(tree_res.second, checker_res.second);
+    return tree_res;
+  }
+  iterator find(const key_type &key) {
+    return iter_check(tree_.find(key), checker_.find(key));
+  }
+  const_iterator find(const key_type &key) const {
+    return iter_check(tree_.find(key), checker_.find(key));
+  }
+  bool contains(const key_type &key) const {
+    return find(key) != end();
+  }
+  size_type count(const key_type &key) const {
+    size_type res = checker_.count(key);
+    EXPECT_EQ(res, tree_.count(key));
+    return res;
+  }
+
+  base_checker &operator=(const base_checker &x) {
+    tree_ = x.tree_;
+    checker_ = x.checker_;
+    return *this;
+  }
+
+  int erase(const key_type &key) {
+    int size = tree_.size();
+    int res = checker_.erase(key);
+    EXPECT_EQ(res, tree_.count(key));
+    EXPECT_EQ(res, tree_.erase(key));
+    EXPECT_EQ(tree_.count(key), 0);
+    EXPECT_EQ(tree_.size(), size - res);
+    erase_check(key);
+    return res;
+  }
+  iterator erase(iterator iter) {
+    key_type key = iter.key();
+    int size = tree_.size();
+    int count = tree_.count(key);
+    auto checker_iter = checker_.lower_bound(key);
+    for (iterator tmp(tree_.lower_bound(key)); tmp != iter; ++tmp) {
+      ++checker_iter;
+    }
+    auto checker_next = checker_iter;
+    ++checker_next;
+    checker_.erase(checker_iter);
+    iter = tree_.erase(iter);
+    EXPECT_EQ(tree_.size(), checker_.size());
+    EXPECT_EQ(tree_.size(), size - 1);
+    EXPECT_EQ(tree_.count(key), count - 1);
+    if (count == 1) {
+      erase_check(key);
+    }
+    return iter_check(iter, checker_next);
+  }
+
+  void erase(iterator begin, iterator end) {
+    int size = tree_.size();
+    int count = std::distance(begin, end);
+    auto checker_begin = checker_.lower_bound(begin.key());
+    for (iterator tmp(tree_.lower_bound(begin.key())); tmp != begin; ++tmp) {
+      ++checker_begin;
+    }
+    auto checker_end =
+        end == tree_.end() ? checker_.end() : checker_.lower_bound(end.key());
+    if (end != tree_.end()) {
+      for (iterator tmp(tree_.lower_bound(end.key())); tmp != end; ++tmp) {
+        ++checker_end;
+      }
+    }
+    checker_.erase(checker_begin, checker_end);
+    tree_.erase(begin, end);
+    EXPECT_EQ(tree_.size(), checker_.size());
+    EXPECT_EQ(tree_.size(), size - count);
+  }
+
+  void clear() {
+    tree_.clear();
+    checker_.clear();
+  }
+  void swap(base_checker &x) {
+    tree_.swap(x.tree_);
+    checker_.swap(x.checker_);
+  }
+
+  void verify() const {
+    tree_.verify();
+    EXPECT_EQ(tree_.size(), checker_.size());
+
+    // Move through the forward iterators using increment.
+    auto checker_iter = checker_.begin();
+    const_iterator tree_iter(tree_.begin());
+    for (; tree_iter != tree_.end(); ++tree_iter, ++checker_iter) {
+      CheckPairEquals(*tree_iter, *checker_iter);
+    }
+
+    // Move through the forward iterators using decrement.
+    for (int n = tree_.size() - 1; n >= 0; --n) {
+      iter_check(tree_iter, checker_iter);
+      --tree_iter;
+      --checker_iter;
+    }
+    EXPECT_EQ(tree_iter, tree_.begin());
+    EXPECT_EQ(checker_iter, checker_.begin());
+
+    // Move through the reverse iterators using increment.
+    auto checker_riter = checker_.rbegin();
+    const_reverse_iterator tree_riter(tree_.rbegin());
+    for (; tree_riter != tree_.rend(); ++tree_riter, ++checker_riter) {
+      CheckPairEquals(*tree_riter, *checker_riter);
+    }
+
+    // Move through the reverse iterators using decrement.
+    for (int n = tree_.size() - 1; n >= 0; --n) {
+      riter_check(tree_riter, checker_riter);
+      --tree_riter;
+      --checker_riter;
+    }
+    EXPECT_EQ(tree_riter, tree_.rbegin());
+    EXPECT_EQ(checker_riter, checker_.rbegin());
+  }
+
+  const TreeType &tree() const { return tree_; }
+
+  size_type size() const {
+    EXPECT_EQ(tree_.size(), checker_.size());
+    return tree_.size();
+  }
+  size_type max_size() const { return tree_.max_size(); }
+  bool empty() const {
+    EXPECT_EQ(tree_.empty(), checker_.empty());
+    return tree_.empty();
+  }
+
+ protected:
+  TreeType tree_;
+  const TreeType &const_tree_;
+  CheckerType checker_;
+};
+
+namespace {
+// A checker for unique sorted associative containers. TreeType is expected to
+// be btree_{set,map} and CheckerType is expected to be {set,map}.
+template <typename TreeType, typename CheckerType>
+class unique_checker : public base_checker<TreeType, CheckerType> {
+  using super_type = base_checker<TreeType, CheckerType>;
+
+ public:
+  using iterator = typename super_type::iterator;
+  using value_type = typename super_type::value_type;
+
+ public:
+  unique_checker() : super_type() {}
+  unique_checker(const unique_checker &x) : super_type(x) {}
+  template <class InputIterator>
+  unique_checker(InputIterator b, InputIterator e) : super_type(b, e) {}
+
+  // Insertion routines.
+  std::pair<iterator, bool> insert(const value_type &x) {
+    int size = this->tree_.size();
+    std::pair<typename CheckerType::iterator, bool> checker_res =
+        this->checker_.insert(x);
+    std::pair<iterator, bool> tree_res = this->tree_.insert(x);
+    CheckPairEquals(*tree_res.first, *checker_res.first);
+    EXPECT_EQ(tree_res.second, checker_res.second);
+    EXPECT_EQ(this->tree_.size(), this->checker_.size());
+    EXPECT_EQ(this->tree_.size(), size + tree_res.second);
+    return tree_res;
+  }
+  iterator insert(iterator position, const value_type &x) {
+    int size = this->tree_.size();
+    std::pair<typename CheckerType::iterator, bool> checker_res =
+        this->checker_.insert(x);
+    iterator tree_res = this->tree_.insert(position, x);
+    CheckPairEquals(*tree_res, *checker_res.first);
+    EXPECT_EQ(this->tree_.size(), this->checker_.size());
+    EXPECT_EQ(this->tree_.size(), size + checker_res.second);
+    return tree_res;
+  }
+  template <typename InputIterator>
+  void insert(InputIterator b, InputIterator e) {
+    for (; b != e; ++b) {
+      insert(*b);
+    }
+  }
+};
+
+// A checker for multiple sorted associative containers. TreeType is expected
+// to be btree_{multiset,multimap} and CheckerType is expected to be
+// {multiset,multimap}.
+template <typename TreeType, typename CheckerType>
+class multi_checker : public base_checker<TreeType, CheckerType> {
+  using super_type = base_checker<TreeType, CheckerType>;
+
+ public:
+  using iterator = typename super_type::iterator;
+  using value_type = typename super_type::value_type;
+
+ public:
+  multi_checker() : super_type() {}
+  multi_checker(const multi_checker &x) : super_type(x) {}
+  template <class InputIterator>
+  multi_checker(InputIterator b, InputIterator e) : super_type(b, e) {}
+
+  // Insertion routines.
+  iterator insert(const value_type &x) {
+    int size = this->tree_.size();
+    auto checker_res = this->checker_.insert(x);
+    iterator tree_res = this->tree_.insert(x);
+    CheckPairEquals(*tree_res, *checker_res);
+    EXPECT_EQ(this->tree_.size(), this->checker_.size());
+    EXPECT_EQ(this->tree_.size(), size + 1);
+    return tree_res;
+  }
+  iterator insert(iterator position, const value_type &x) {
+    int size = this->tree_.size();
+    auto checker_res = this->checker_.insert(x);
+    iterator tree_res = this->tree_.insert(position, x);
+    CheckPairEquals(*tree_res, *checker_res);
+    EXPECT_EQ(this->tree_.size(), this->checker_.size());
+    EXPECT_EQ(this->tree_.size(), size + 1);
+    return tree_res;
+  }
+  template <typename InputIterator>
+  void insert(InputIterator b, InputIterator e) {
+    for (; b != e; ++b) {
+      insert(*b);
+    }
+  }
+};
+
+template <typename T, typename V>
+void DoTest(const char *name, T *b, const std::vector<V> &values) {
+  typename KeyOfValue<typename T::key_type, V>::type key_of_value;
+
+  T &mutable_b = *b;
+  const T &const_b = *b;
+
+  // Test insert.
+  for (int i = 0; i < values.size(); ++i) {
+    mutable_b.insert(values[i]);
+    mutable_b.value_check(values[i]);
+  }
+  ASSERT_EQ(mutable_b.size(), values.size());
+
+  const_b.verify();
+
+  // Test copy constructor.
+  T b_copy(const_b);
+  EXPECT_EQ(b_copy.size(), const_b.size());
+  for (int i = 0; i < values.size(); ++i) {
+    CheckPairEquals(*b_copy.find(key_of_value(values[i])), values[i]);
+  }
+
+  // Test range constructor.
+  T b_range(const_b.begin(), const_b.end());
+  EXPECT_EQ(b_range.size(), const_b.size());
+  for (int i = 0; i < values.size(); ++i) {
+    CheckPairEquals(*b_range.find(key_of_value(values[i])), values[i]);
+  }
+
+  // Test range insertion for values that already exist.
+  b_range.insert(b_copy.begin(), b_copy.end());
+  b_range.verify();
+
+  // Test range insertion for new values.
+  b_range.clear();
+  b_range.insert(b_copy.begin(), b_copy.end());
+  EXPECT_EQ(b_range.size(), b_copy.size());
+  for (int i = 0; i < values.size(); ++i) {
+    CheckPairEquals(*b_range.find(key_of_value(values[i])), values[i]);
+  }
+
+  // Test assignment to self. Nothing should change.
+  b_range.operator=(b_range);
+  EXPECT_EQ(b_range.size(), b_copy.size());
+
+  // Test assignment of new values.
+  b_range.clear();
+  b_range = b_copy;
+  EXPECT_EQ(b_range.size(), b_copy.size());
+
+  // Test swap.
+  b_range.clear();
+  b_range.swap(b_copy);
+  EXPECT_EQ(b_copy.size(), 0);
+  EXPECT_EQ(b_range.size(), const_b.size());
+  for (int i = 0; i < values.size(); ++i) {
+    CheckPairEquals(*b_range.find(key_of_value(values[i])), values[i]);
+  }
+  b_range.swap(b_copy);
+
+  // Test non-member function swap.
+  swap(b_range, b_copy);
+  EXPECT_EQ(b_copy.size(), 0);
+  EXPECT_EQ(b_range.size(), const_b.size());
+  for (int i = 0; i < values.size(); ++i) {
+    CheckPairEquals(*b_range.find(key_of_value(values[i])), values[i]);
+  }
+  swap(b_range, b_copy);
+
+  // Test erase via values.
+  for (int i = 0; i < values.size(); ++i) {
+    mutable_b.erase(key_of_value(values[i]));
+    // Erasing a non-existent key should have no effect.
+    ASSERT_EQ(mutable_b.erase(key_of_value(values[i])), 0);
+  }
+
+  const_b.verify();
+  EXPECT_EQ(const_b.size(), 0);
+
+  // Test erase via iterators.
+  mutable_b = b_copy;
+  for (int i = 0; i < values.size(); ++i) {
+    mutable_b.erase(mutable_b.find(key_of_value(values[i])));
+  }
+
+  const_b.verify();
+  EXPECT_EQ(const_b.size(), 0);
+
+  // Test insert with hint.
+  for (int i = 0; i < values.size(); i++) {
+    mutable_b.insert(mutable_b.upper_bound(key_of_value(values[i])), values[i]);
+  }
+
+  const_b.verify();
+
+  // Test range erase.
+  mutable_b.erase(mutable_b.begin(), mutable_b.end());
+  EXPECT_EQ(mutable_b.size(), 0);
+  const_b.verify();
+
+  // First half.
+  mutable_b = b_copy;
+  typename T::iterator mutable_iter_end = mutable_b.begin();
+  for (int i = 0; i < values.size() / 2; ++i) ++mutable_iter_end;
+  mutable_b.erase(mutable_b.begin(), mutable_iter_end);
+  EXPECT_EQ(mutable_b.size(), values.size() - values.size() / 2);
+  const_b.verify();
+
+  // Second half.
+  mutable_b = b_copy;
+  typename T::iterator mutable_iter_begin = mutable_b.begin();
+  for (int i = 0; i < values.size() / 2; ++i) ++mutable_iter_begin;
+  mutable_b.erase(mutable_iter_begin, mutable_b.end());
+  EXPECT_EQ(mutable_b.size(), values.size() / 2);
+  const_b.verify();
+
+  // Second quarter.
+  mutable_b = b_copy;
+  mutable_iter_begin = mutable_b.begin();
+  for (int i = 0; i < values.size() / 4; ++i) ++mutable_iter_begin;
+  mutable_iter_end = mutable_iter_begin;
+  for (int i = 0; i < values.size() / 4; ++i) ++mutable_iter_end;
+  mutable_b.erase(mutable_iter_begin, mutable_iter_end);
+  EXPECT_EQ(mutable_b.size(), values.size() - values.size() / 4);
+  const_b.verify();
+
+  mutable_b.clear();
+}
+
+template <typename T>
+void ConstTest() {
+  using value_type = typename T::value_type;
+  typename KeyOfValue<typename T::key_type, value_type>::type key_of_value;
+
+  T mutable_b;
+  const T &const_b = mutable_b;
+
+  // Insert a single value into the container and test looking it up.
+  value_type value = Generator<value_type>(2)(2);
+  mutable_b.insert(value);
+  EXPECT_TRUE(mutable_b.contains(key_of_value(value)));
+  EXPECT_NE(mutable_b.find(key_of_value(value)), const_b.end());
+  EXPECT_TRUE(const_b.contains(key_of_value(value)));
+  EXPECT_NE(const_b.find(key_of_value(value)), mutable_b.end());
+  EXPECT_EQ(*const_b.lower_bound(key_of_value(value)), value);
+  EXPECT_EQ(const_b.upper_bound(key_of_value(value)), const_b.end());
+  EXPECT_EQ(*const_b.equal_range(key_of_value(value)).first, value);
+
+  // We can only create a non-const iterator from a non-const container.
+  typename T::iterator mutable_iter(mutable_b.begin());
+  EXPECT_EQ(mutable_iter, const_b.begin());
+  EXPECT_NE(mutable_iter, const_b.end());
+  EXPECT_EQ(const_b.begin(), mutable_iter);
+  EXPECT_NE(const_b.end(), mutable_iter);
+  typename T::reverse_iterator mutable_riter(mutable_b.rbegin());
+  EXPECT_EQ(mutable_riter, const_b.rbegin());
+  EXPECT_NE(mutable_riter, const_b.rend());
+  EXPECT_EQ(const_b.rbegin(), mutable_riter);
+  EXPECT_NE(const_b.rend(), mutable_riter);
+
+  // We can create a const iterator from a non-const iterator.
+  typename T::const_iterator const_iter(mutable_iter);
+  EXPECT_EQ(const_iter, mutable_b.begin());
+  EXPECT_NE(const_iter, mutable_b.end());
+  EXPECT_EQ(mutable_b.begin(), const_iter);
+  EXPECT_NE(mutable_b.end(), const_iter);
+  typename T::const_reverse_iterator const_riter(mutable_riter);
+  EXPECT_EQ(const_riter, mutable_b.rbegin());
+  EXPECT_NE(const_riter, mutable_b.rend());
+  EXPECT_EQ(mutable_b.rbegin(), const_riter);
+  EXPECT_NE(mutable_b.rend(), const_riter);
+
+  // Make sure various methods can be invoked on a const container.
+  const_b.verify();
+  ASSERT_TRUE(!const_b.empty());
+  EXPECT_EQ(const_b.size(), 1);
+  EXPECT_GT(const_b.max_size(), 0);
+  EXPECT_TRUE(const_b.contains(key_of_value(value)));
+  EXPECT_EQ(const_b.count(key_of_value(value)), 1);
+}
+
+template <typename T, typename C>
+void BtreeTest() {
+  ConstTest<T>();
+
+  using V = typename remove_pair_const<typename T::value_type>::type;
+  const std::vector<V> random_values = GenerateValuesWithSeed<V>(
+      absl::GetFlag(FLAGS_test_values), 4 * absl::GetFlag(FLAGS_test_values),
+      testing::GTEST_FLAG(random_seed));
+
+  unique_checker<T, C> container;
+
+  // Test key insertion/deletion in sorted order.
+  std::vector<V> sorted_values(random_values);
+  std::sort(sorted_values.begin(), sorted_values.end());
+  DoTest("sorted:    ", &container, sorted_values);
+
+  // Test key insertion/deletion in reverse sorted order.
+  std::reverse(sorted_values.begin(), sorted_values.end());
+  DoTest("rsorted:   ", &container, sorted_values);
+
+  // Test key insertion/deletion in random order.
+  DoTest("random:    ", &container, random_values);
+}
+
+template <typename T, typename C>
+void BtreeMultiTest() {
+  ConstTest<T>();
+
+  using V = typename remove_pair_const<typename T::value_type>::type;
+  const std::vector<V> random_values = GenerateValuesWithSeed<V>(
+      absl::GetFlag(FLAGS_test_values), 4 * absl::GetFlag(FLAGS_test_values),
+      testing::GTEST_FLAG(random_seed));
+
+  multi_checker<T, C> container;
+
+  // Test keys in sorted order.
+  std::vector<V> sorted_values(random_values);
+  std::sort(sorted_values.begin(), sorted_values.end());
+  DoTest("sorted:    ", &container, sorted_values);
+
+  // Test keys in reverse sorted order.
+  std::reverse(sorted_values.begin(), sorted_values.end());
+  DoTest("rsorted:   ", &container, sorted_values);
+
+  // Test keys in random order.
+  DoTest("random:    ", &container, random_values);
+
+  // Test keys in random order w/ duplicates.
+  std::vector<V> duplicate_values(random_values);
+  duplicate_values.insert(duplicate_values.end(), random_values.begin(),
+                          random_values.end());
+  DoTest("duplicates:", &container, duplicate_values);
+
+  // Test all identical keys.
+  std::vector<V> identical_values(100);
+  std::fill(identical_values.begin(), identical_values.end(),
+            Generator<V>(2)(2));
+  DoTest("identical: ", &container, identical_values);
+}
+
+template <typename T>
+struct PropagatingCountingAlloc : public CountingAllocator<T> {
+  using propagate_on_container_copy_assignment = std::true_type;
+  using propagate_on_container_move_assignment = std::true_type;
+  using propagate_on_container_swap = std::true_type;
+
+  using Base = CountingAllocator<T>;
+  using Base::Base;
+
+  template <typename U>
+  explicit PropagatingCountingAlloc(const PropagatingCountingAlloc<U> &other)
+      : Base(other.bytes_used_) {}
+
+  template <typename U>
+  struct rebind {
+    using other = PropagatingCountingAlloc<U>;
+  };
+};
+
+template <typename T>
+void BtreeAllocatorTest() {
+  using value_type = typename T::value_type;
+
+  int64_t bytes1 = 0, bytes2 = 0;
+  PropagatingCountingAlloc<T> allocator1(&bytes1);
+  PropagatingCountingAlloc<T> allocator2(&bytes2);
+  Generator<value_type> generator(1000);
+
+  // Test that we allocate properly aligned memory. If we don't, then Layout
+  // will assert fail.
+  auto unused1 = allocator1.allocate(1);
+  auto unused2 = allocator2.allocate(1);
+
+  // Test copy assignment
+  {
+    T b1(typename T::key_compare(), allocator1);
+    T b2(typename T::key_compare(), allocator2);
+
+    int64_t original_bytes1 = bytes1;
+    b1.insert(generator(0));
+    EXPECT_GT(bytes1, original_bytes1);
+
+    // This should propagate the allocator.
+    b1 = b2;
+    EXPECT_EQ(b1.size(), 0);
+    EXPECT_EQ(b2.size(), 0);
+    EXPECT_EQ(bytes1, original_bytes1);
+
+    for (int i = 1; i < 1000; i++) {
+      b1.insert(generator(i));
+    }
+
+    // We should have allocated out of allocator2.
+    EXPECT_GT(bytes2, bytes1);
+  }
+
+  // Test move assignment
+  {
+    T b1(typename T::key_compare(), allocator1);
+    T b2(typename T::key_compare(), allocator2);
+
+    int64_t original_bytes1 = bytes1;
+    b1.insert(generator(0));
+    EXPECT_GT(bytes1, original_bytes1);
+
+    // This should propagate the allocator.
+    b1 = std::move(b2);
+    EXPECT_EQ(b1.size(), 0);
+    EXPECT_EQ(bytes1, original_bytes1);
+
+    for (int i = 1; i < 1000; i++) {
+      b1.insert(generator(i));
+    }
+
+    // We should have allocated out of allocator2.
+    EXPECT_GT(bytes2, bytes1);
+  }
+
+  // Test swap
+  {
+    T b1(typename T::key_compare(), allocator1);
+    T b2(typename T::key_compare(), allocator2);
+
+    int64_t original_bytes1 = bytes1;
+    b1.insert(generator(0));
+    EXPECT_GT(bytes1, original_bytes1);
+
+    // This should swap the allocators.
+    swap(b1, b2);
+    EXPECT_EQ(b1.size(), 0);
+    EXPECT_EQ(b2.size(), 1);
+    EXPECT_GT(bytes1, original_bytes1);
+
+    for (int i = 1; i < 1000; i++) {
+      b1.insert(generator(i));
+    }
+
+    // We should have allocated out of allocator2.
+    EXPECT_GT(bytes2, bytes1);
+  }
+
+  allocator1.deallocate(unused1, 1);
+  allocator2.deallocate(unused2, 1);
+}
+
+template <typename T>
+void BtreeMapTest() {
+  using value_type = typename T::value_type;
+  using mapped_type = typename T::mapped_type;
+
+  mapped_type m = Generator<mapped_type>(0)(0);
+  (void)m;
+
+  T b;
+
+  // Verify we can insert using operator[].
+  for (int i = 0; i < 1000; i++) {
+    value_type v = Generator<value_type>(1000)(i);
+    b[v.first] = v.second;
+  }
+  EXPECT_EQ(b.size(), 1000);
+
+  // Test whether we can use the "->" operator on iterators and
+  // reverse_iterators. This stresses the btree_map_params::pair_pointer
+  // mechanism.
+  EXPECT_EQ(b.begin()->first, Generator<value_type>(1000)(0).first);
+  EXPECT_EQ(b.begin()->second, Generator<value_type>(1000)(0).second);
+  EXPECT_EQ(b.rbegin()->first, Generator<value_type>(1000)(999).first);
+  EXPECT_EQ(b.rbegin()->second, Generator<value_type>(1000)(999).second);
+}
+
+template <typename T>
+void BtreeMultiMapTest() {
+  using mapped_type = typename T::mapped_type;
+  mapped_type m = Generator<mapped_type>(0)(0);
+  (void)m;
+}
+
+template <typename K, int N = 256>
+void SetTest() {
+  EXPECT_EQ(
+      sizeof(absl::btree_set<K>),
+      2 * sizeof(void *) + sizeof(typename absl::btree_set<K>::size_type));
+  using BtreeSet = absl::btree_set<K>;
+  using CountingBtreeSet =
+      absl::btree_set<K, std::less<K>, PropagatingCountingAlloc<K>>;
+  BtreeTest<BtreeSet, std::set<K>>();
+  BtreeAllocatorTest<CountingBtreeSet>();
+}
+
+template <typename K, int N = 256>
+void MapTest() {
+  EXPECT_EQ(
+      sizeof(absl::btree_map<K, K>),
+      2 * sizeof(void *) + sizeof(typename absl::btree_map<K, K>::size_type));
+  using BtreeMap = absl::btree_map<K, K>;
+  using CountingBtreeMap =
+      absl::btree_map<K, K, std::less<K>,
+                      PropagatingCountingAlloc<std::pair<const K, K>>>;
+  BtreeTest<BtreeMap, std::map<K, K>>();
+  BtreeAllocatorTest<CountingBtreeMap>();
+  BtreeMapTest<BtreeMap>();
+}
+
+TEST(Btree, set_int32) { SetTest<int32_t>(); }
+TEST(Btree, set_int64) { SetTest<int64_t>(); }
+TEST(Btree, set_string) { SetTest<std::string>(); }
+TEST(Btree, set_pair) { SetTest<std::pair<int, int>>(); }
+TEST(Btree, map_int32) { MapTest<int32_t>(); }
+TEST(Btree, map_int64) { MapTest<int64_t>(); }
+TEST(Btree, map_string) { MapTest<std::string>(); }
+TEST(Btree, map_pair) { MapTest<std::pair<int, int>>(); }
+
+template <typename K, int N = 256>
+void MultiSetTest() {
+  EXPECT_EQ(
+      sizeof(absl::btree_multiset<K>),
+      2 * sizeof(void *) + sizeof(typename absl::btree_multiset<K>::size_type));
+  using BtreeMSet = absl::btree_multiset<K>;
+  using CountingBtreeMSet =
+      absl::btree_multiset<K, std::less<K>, PropagatingCountingAlloc<K>>;
+  BtreeMultiTest<BtreeMSet, std::multiset<K>>();
+  BtreeAllocatorTest<CountingBtreeMSet>();
+}
+
+template <typename K, int N = 256>
+void MultiMapTest() {
+  EXPECT_EQ(sizeof(absl::btree_multimap<K, K>),
+            2 * sizeof(void *) +
+                sizeof(typename absl::btree_multimap<K, K>::size_type));
+  using BtreeMMap = absl::btree_multimap<K, K>;
+  using CountingBtreeMMap =
+      absl::btree_multimap<K, K, std::less<K>,
+                           PropagatingCountingAlloc<std::pair<const K, K>>>;
+  BtreeMultiTest<BtreeMMap, std::multimap<K, K>>();
+  BtreeMultiMapTest<BtreeMMap>();
+  BtreeAllocatorTest<CountingBtreeMMap>();
+}
+
+TEST(Btree, multiset_int32) { MultiSetTest<int32_t>(); }
+TEST(Btree, multiset_int64) { MultiSetTest<int64_t>(); }
+TEST(Btree, multiset_string) { MultiSetTest<std::string>(); }
+TEST(Btree, multiset_pair) { MultiSetTest<std::pair<int, int>>(); }
+TEST(Btree, multimap_int32) { MultiMapTest<int32_t>(); }
+TEST(Btree, multimap_int64) { MultiMapTest<int64_t>(); }
+TEST(Btree, multimap_string) { MultiMapTest<std::string>(); }
+TEST(Btree, multimap_pair) { MultiMapTest<std::pair<int, int>>(); }
+
+struct CompareIntToString {
+  bool operator()(const std::string &a, const std::string &b) const {
+    return a < b;
+  }
+  bool operator()(const std::string &a, int b) const {
+    return a < absl::StrCat(b);
+  }
+  bool operator()(int a, const std::string &b) const {
+    return absl::StrCat(a) < b;
+  }
+  using is_transparent = void;
+};
+
+struct NonTransparentCompare {
+  template <typename T, typename U>
+  bool operator()(const T& t, const U& u) const {
+    // Treating all comparators as transparent can cause inefficiencies (see
+    // N3657 C++ proposal). Test that for comparators without 'is_transparent'
+    // alias (like this one), we do not attempt heterogeneous lookup.
+    EXPECT_TRUE((std::is_same<T, U>()));
+    return t < u;
+  }
+};
+
+template <typename T>
+bool CanEraseWithEmptyBrace(T t, decltype(t.erase({})) *) {
+  return true;
+}
+
+template <typename T>
+bool CanEraseWithEmptyBrace(T, ...) {
+  return false;
+}
+
+template <typename T>
+void TestHeterogeneous(T table) {
+  auto lb = table.lower_bound("3");
+  EXPECT_EQ(lb, table.lower_bound(3));
+  EXPECT_NE(lb, table.lower_bound(4));
+  EXPECT_EQ(lb, table.lower_bound({"3"}));
+  EXPECT_NE(lb, table.lower_bound({}));
+
+  auto ub = table.upper_bound("3");
+  EXPECT_EQ(ub, table.upper_bound(3));
+  EXPECT_NE(ub, table.upper_bound(5));
+  EXPECT_EQ(ub, table.upper_bound({"3"}));
+  EXPECT_NE(ub, table.upper_bound({}));
+
+  auto er = table.equal_range("3");
+  EXPECT_EQ(er, table.equal_range(3));
+  EXPECT_NE(er, table.equal_range(4));
+  EXPECT_EQ(er, table.equal_range({"3"}));
+  EXPECT_NE(er, table.equal_range({}));
+
+  auto it = table.find("3");
+  EXPECT_EQ(it, table.find(3));
+  EXPECT_NE(it, table.find(4));
+  EXPECT_EQ(it, table.find({"3"}));
+  EXPECT_NE(it, table.find({}));
+
+  EXPECT_TRUE(table.contains(3));
+  EXPECT_FALSE(table.contains(4));
+  EXPECT_TRUE(table.count({"3"}));
+  EXPECT_FALSE(table.contains({}));
+
+  EXPECT_EQ(1, table.count(3));
+  EXPECT_EQ(0, table.count(4));
+  EXPECT_EQ(1, table.count({"3"}));
+  EXPECT_EQ(0, table.count({}));
+
+  auto copy = table;
+  copy.erase(3);
+  EXPECT_EQ(table.size() - 1, copy.size());
+  copy.erase(4);
+  EXPECT_EQ(table.size() - 1, copy.size());
+  copy.erase({"5"});
+  EXPECT_EQ(table.size() - 2, copy.size());
+  EXPECT_FALSE(CanEraseWithEmptyBrace(table, nullptr));
+
+  // Also run it with const T&.
+  if (std::is_class<T>()) TestHeterogeneous<const T &>(table);
+}
+
+TEST(Btree, HeterogeneousLookup) {
+  TestHeterogeneous(btree_set<std::string, CompareIntToString>{"1", "3", "5"});
+  TestHeterogeneous(btree_map<std::string, int, CompareIntToString>{
+      {"1", 1}, {"3", 3}, {"5", 5}});
+  TestHeterogeneous(
+      btree_multiset<std::string, CompareIntToString>{"1", "3", "5"});
+  TestHeterogeneous(btree_multimap<std::string, int, CompareIntToString>{
+      {"1", 1}, {"3", 3}, {"5", 5}});
+
+  // Only maps have .at()
+  btree_map<std::string, int, CompareIntToString> map{
+      {"", -1}, {"1", 1}, {"3", 3}, {"5", 5}};
+  EXPECT_EQ(1, map.at(1));
+  EXPECT_EQ(3, map.at({"3"}));
+  EXPECT_EQ(-1, map.at({}));
+  const auto &cmap = map;
+  EXPECT_EQ(1, cmap.at(1));
+  EXPECT_EQ(3, cmap.at({"3"}));
+  EXPECT_EQ(-1, cmap.at({}));
+}
+
+TEST(Btree, NoHeterogeneousLookupWithoutAlias) {
+  using StringSet = absl::btree_set<std::string, NonTransparentCompare>;
+  StringSet s;
+  ASSERT_TRUE(s.insert("hello").second);
+  ASSERT_TRUE(s.insert("world").second);
+  EXPECT_TRUE(s.end() == s.find("blah"));
+  EXPECT_TRUE(s.begin() == s.lower_bound("hello"));
+  EXPECT_EQ(1, s.count("world"));
+  EXPECT_TRUE(s.contains("hello"));
+  EXPECT_TRUE(s.contains("world"));
+  EXPECT_FALSE(s.contains("blah"));
+
+  using StringMultiSet =
+      absl::btree_multiset<std::string, NonTransparentCompare>;
+  StringMultiSet ms;
+  ms.insert("hello");
+  ms.insert("world");
+  ms.insert("world");
+  EXPECT_TRUE(ms.end() == ms.find("blah"));
+  EXPECT_TRUE(ms.begin() == ms.lower_bound("hello"));
+  EXPECT_EQ(2, ms.count("world"));
+  EXPECT_TRUE(ms.contains("hello"));
+  EXPECT_TRUE(ms.contains("world"));
+  EXPECT_FALSE(ms.contains("blah"));
+}
+
+TEST(Btree, DefaultTransparent) {
+  {
+    // `int` does not have a default transparent comparator.
+    // The input value is converted to key_type.
+    btree_set<int> s = {1};
+    double d = 1.1;
+    EXPECT_EQ(s.begin(), s.find(d));
+    EXPECT_TRUE(s.contains(d));
+  }
+
+  {
+    // `std::string` has heterogeneous support.
+    btree_set<std::string> s = {"A"};
+    EXPECT_EQ(s.begin(), s.find(absl::string_view("A")));
+    EXPECT_TRUE(s.contains(absl::string_view("A")));
+  }
+}
+
+class StringLike {
+ public:
+  StringLike() = default;
+
+  StringLike(const char* s) : s_(s) {  // NOLINT
+    ++constructor_calls_;
+  }
+
+  bool operator<(const StringLike& a) const {
+    return s_ < a.s_;
+  }
+
+  static void clear_constructor_call_count() {
+    constructor_calls_ = 0;
+  }
+
+  static int constructor_calls() {
+    return constructor_calls_;
+  }
+
+ private:
+  static int constructor_calls_;
+  std::string s_;
+};
+
+int StringLike::constructor_calls_ = 0;
+
+TEST(Btree, HeterogeneousLookupDoesntDegradePerformance) {
+  using StringSet = absl::btree_set<StringLike>;
+  StringSet s;
+  for (int i = 0; i < 100; ++i) {
+    ASSERT_TRUE(s.insert(absl::StrCat(i).c_str()).second);
+  }
+  StringLike::clear_constructor_call_count();
+  s.find("50");
+  ASSERT_EQ(1, StringLike::constructor_calls());
+
+  StringLike::clear_constructor_call_count();
+  s.contains("50");
+  ASSERT_EQ(1, StringLike::constructor_calls());
+
+  StringLike::clear_constructor_call_count();
+  s.count("50");
+  ASSERT_EQ(1, StringLike::constructor_calls());
+
+  StringLike::clear_constructor_call_count();
+  s.lower_bound("50");
+  ASSERT_EQ(1, StringLike::constructor_calls());
+
+  StringLike::clear_constructor_call_count();
+  s.upper_bound("50");
+  ASSERT_EQ(1, StringLike::constructor_calls());
+
+  StringLike::clear_constructor_call_count();
+  s.equal_range("50");
+  ASSERT_EQ(1, StringLike::constructor_calls());
+
+  StringLike::clear_constructor_call_count();
+  s.erase("50");
+  ASSERT_EQ(1, StringLike::constructor_calls());
+}
+
+// Verify that swapping btrees swaps the key comparison functors and that we can
+// use non-default constructible comparators.
+struct SubstringLess {
+  SubstringLess() = delete;
+  explicit SubstringLess(int length) : n(length) {}
+  bool operator()(const std::string &a, const std::string &b) const {
+    return absl::string_view(a).substr(0, n) <
+           absl::string_view(b).substr(0, n);
+  }
+  int n;
+};
+
+TEST(Btree, SwapKeyCompare) {
+  using SubstringSet = absl::btree_set<std::string, SubstringLess>;
+  SubstringSet s1(SubstringLess(1), SubstringSet::allocator_type());
+  SubstringSet s2(SubstringLess(2), SubstringSet::allocator_type());
+
+  ASSERT_TRUE(s1.insert("a").second);
+  ASSERT_FALSE(s1.insert("aa").second);
+
+  ASSERT_TRUE(s2.insert("a").second);
+  ASSERT_TRUE(s2.insert("aa").second);
+  ASSERT_FALSE(s2.insert("aaa").second);
+
+  swap(s1, s2);
+
+  ASSERT_TRUE(s1.insert("b").second);
+  ASSERT_TRUE(s1.insert("bb").second);
+  ASSERT_FALSE(s1.insert("bbb").second);
+
+  ASSERT_TRUE(s2.insert("b").second);
+  ASSERT_FALSE(s2.insert("bb").second);
+}
+
+TEST(Btree, UpperBoundRegression) {
+  // Regress a bug where upper_bound would default-construct a new key_compare
+  // instead of copying the existing one.
+  using SubstringSet = absl::btree_set<std::string, SubstringLess>;
+  SubstringSet my_set(SubstringLess(3));
+  my_set.insert("aab");
+  my_set.insert("abb");
+  // We call upper_bound("aaa").  If this correctly uses the length 3
+  // comparator, aaa < aab < abb, so we should get aab as the result.
+  // If it instead uses the default-constructed length 2 comparator,
+  // aa == aa < ab, so we'll get abb as our result.
+  SubstringSet::iterator it = my_set.upper_bound("aaa");
+  ASSERT_TRUE(it != my_set.end());
+  EXPECT_EQ("aab", *it);
+}
+
+TEST(Btree, Comparison) {
+  const int kSetSize = 1201;
+  absl::btree_set<int64_t> my_set;
+  for (int i = 0; i < kSetSize; ++i) {
+    my_set.insert(i);
+  }
+  absl::btree_set<int64_t> my_set_copy(my_set);
+  EXPECT_TRUE(my_set_copy == my_set);
+  EXPECT_TRUE(my_set == my_set_copy);
+  EXPECT_FALSE(my_set_copy != my_set);
+  EXPECT_FALSE(my_set != my_set_copy);
+
+  my_set.insert(kSetSize);
+  EXPECT_FALSE(my_set_copy == my_set);
+  EXPECT_FALSE(my_set == my_set_copy);
+  EXPECT_TRUE(my_set_copy != my_set);
+  EXPECT_TRUE(my_set != my_set_copy);
+
+  my_set.erase(kSetSize - 1);
+  EXPECT_FALSE(my_set_copy == my_set);
+  EXPECT_FALSE(my_set == my_set_copy);
+  EXPECT_TRUE(my_set_copy != my_set);
+  EXPECT_TRUE(my_set != my_set_copy);
+
+  absl::btree_map<std::string, int64_t> my_map;
+  for (int i = 0; i < kSetSize; ++i) {
+    my_map[std::string(i, 'a')] = i;
+  }
+  absl::btree_map<std::string, int64_t> my_map_copy(my_map);
+  EXPECT_TRUE(my_map_copy == my_map);
+  EXPECT_TRUE(my_map == my_map_copy);
+  EXPECT_FALSE(my_map_copy != my_map);
+  EXPECT_FALSE(my_map != my_map_copy);
+
+  ++my_map_copy[std::string(7, 'a')];
+  EXPECT_FALSE(my_map_copy == my_map);
+  EXPECT_FALSE(my_map == my_map_copy);
+  EXPECT_TRUE(my_map_copy != my_map);
+  EXPECT_TRUE(my_map != my_map_copy);
+
+  my_map_copy = my_map;
+  my_map["hello"] = kSetSize;
+  EXPECT_FALSE(my_map_copy == my_map);
+  EXPECT_FALSE(my_map == my_map_copy);
+  EXPECT_TRUE(my_map_copy != my_map);
+  EXPECT_TRUE(my_map != my_map_copy);
+
+  my_map.erase(std::string(kSetSize - 1, 'a'));
+  EXPECT_FALSE(my_map_copy == my_map);
+  EXPECT_FALSE(my_map == my_map_copy);
+  EXPECT_TRUE(my_map_copy != my_map);
+  EXPECT_TRUE(my_map != my_map_copy);
+}
+
+TEST(Btree, RangeCtorSanity) {
+  std::vector<int> ivec;
+  ivec.push_back(1);
+  std::map<int, int> imap;
+  imap.insert(std::make_pair(1, 2));
+  absl::btree_multiset<int> tmset(ivec.begin(), ivec.end());
+  absl::btree_multimap<int, int> tmmap(imap.begin(), imap.end());
+  absl::btree_set<int> tset(ivec.begin(), ivec.end());
+  absl::btree_map<int, int> tmap(imap.begin(), imap.end());
+  EXPECT_EQ(1, tmset.size());
+  EXPECT_EQ(1, tmmap.size());
+  EXPECT_EQ(1, tset.size());
+  EXPECT_EQ(1, tmap.size());
+}
+
+TEST(Btree, BtreeMapCanHoldMoveOnlyTypes) {
+  absl::btree_map<std::string, std::unique_ptr<std::string>> m;
+
+  std::unique_ptr<std::string> &v = m["A"];
+  EXPECT_TRUE(v == nullptr);
+  v.reset(new std::string("X"));
+
+  auto iter = m.find("A");
+  EXPECT_EQ("X", *iter->second);
+}
+
+TEST(Btree, InitializerListConstructor) {
+  absl::btree_set<std::string> set({"a", "b"});
+  EXPECT_EQ(set.count("a"), 1);
+  EXPECT_EQ(set.count("b"), 1);
+
+  absl::btree_multiset<int> mset({1, 1, 4});
+  EXPECT_EQ(mset.count(1), 2);
+  EXPECT_EQ(mset.count(4), 1);
+
+  absl::btree_map<int, int> map({{1, 5}, {2, 10}});
+  EXPECT_EQ(map[1], 5);
+  EXPECT_EQ(map[2], 10);
+
+  absl::btree_multimap<int, int> mmap({{1, 5}, {1, 10}});
+  auto range = mmap.equal_range(1);
+  auto it = range.first;
+  ASSERT_NE(it, range.second);
+  EXPECT_EQ(it->second, 5);
+  ASSERT_NE(++it, range.second);
+  EXPECT_EQ(it->second, 10);
+  EXPECT_EQ(++it, range.second);
+}
+
+TEST(Btree, InitializerListInsert) {
+  absl::btree_set<std::string> set;
+  set.insert({"a", "b"});
+  EXPECT_EQ(set.count("a"), 1);
+  EXPECT_EQ(set.count("b"), 1);
+
+  absl::btree_multiset<int> mset;
+  mset.insert({1, 1, 4});
+  EXPECT_EQ(mset.count(1), 2);
+  EXPECT_EQ(mset.count(4), 1);
+
+  absl::btree_map<int, int> map;
+  map.insert({{1, 5}, {2, 10}});
+  // Test that inserting one element using an initializer list also works.
+  map.insert({3, 15});
+  EXPECT_EQ(map[1], 5);
+  EXPECT_EQ(map[2], 10);
+  EXPECT_EQ(map[3], 15);
+
+  absl::btree_multimap<int, int> mmap;
+  mmap.insert({{1, 5}, {1, 10}});
+  auto range = mmap.equal_range(1);
+  auto it = range.first;
+  ASSERT_NE(it, range.second);
+  EXPECT_EQ(it->second, 5);
+  ASSERT_NE(++it, range.second);
+  EXPECT_EQ(it->second, 10);
+  EXPECT_EQ(++it, range.second);
+}
+
+template <typename Compare, typename K>
+void AssertKeyCompareToAdapted() {
+  using Adapted = typename key_compare_to_adapter<Compare>::type;
+  static_assert(!std::is_same<Adapted, Compare>::value,
+                "key_compare_to_adapter should have adapted this comparator.");
+  static_assert(
+      std::is_same<absl::weak_ordering,
+                   absl::result_of_t<Adapted(const K &, const K &)>>::value,
+      "Adapted comparator should be a key-compare-to comparator.");
+}
+template <typename Compare, typename K>
+void AssertKeyCompareToNotAdapted() {
+  using Unadapted = typename key_compare_to_adapter<Compare>::type;
+  static_assert(
+      std::is_same<Unadapted, Compare>::value,
+      "key_compare_to_adapter shouldn't have adapted this comparator.");
+  static_assert(
+      std::is_same<bool,
+                   absl::result_of_t<Unadapted(const K &, const K &)>>::value,
+      "Un-adapted comparator should return bool.");
+}
+
+TEST(Btree, KeyCompareToAdapter) {
+  AssertKeyCompareToAdapted<std::less<std::string>, std::string>();
+  AssertKeyCompareToAdapted<std::greater<std::string>, std::string>();
+  AssertKeyCompareToAdapted<std::less<absl::string_view>, absl::string_view>();
+  AssertKeyCompareToAdapted<std::greater<absl::string_view>,
+                            absl::string_view>();
+  AssertKeyCompareToNotAdapted<std::less<int>, int>();
+  AssertKeyCompareToNotAdapted<std::greater<int>, int>();
+}
+
+TEST(Btree, RValueInsert) {
+  InstanceTracker tracker;
+
+  absl::btree_set<MovableOnlyInstance> set;
+  set.insert(MovableOnlyInstance(1));
+  set.insert(MovableOnlyInstance(3));
+  MovableOnlyInstance two(2);
+  set.insert(set.find(MovableOnlyInstance(3)), std::move(two));
+  auto it = set.find(MovableOnlyInstance(2));
+  ASSERT_NE(it, set.end());
+  ASSERT_NE(++it, set.end());
+  EXPECT_EQ(it->value(), 3);
+
+  absl::btree_multiset<MovableOnlyInstance> mset;
+  MovableOnlyInstance zero(0);
+  MovableOnlyInstance zero2(0);
+  mset.insert(std::move(zero));
+  mset.insert(mset.find(MovableOnlyInstance(0)), std::move(zero2));
+  EXPECT_EQ(mset.count(MovableOnlyInstance(0)), 2);
+
+  absl::btree_map<int, MovableOnlyInstance> map;
+  std::pair<const int, MovableOnlyInstance> p1 = {1, MovableOnlyInstance(5)};
+  std::pair<const int, MovableOnlyInstance> p2 = {2, MovableOnlyInstance(10)};
+  std::pair<const int, MovableOnlyInstance> p3 = {3, MovableOnlyInstance(15)};
+  map.insert(std::move(p1));
+  map.insert(std::move(p3));
+  map.insert(map.find(3), std::move(p2));
+  ASSERT_NE(map.find(2), map.end());
+  EXPECT_EQ(map.find(2)->second.value(), 10);
+
+  absl::btree_multimap<int, MovableOnlyInstance> mmap;
+  std::pair<const int, MovableOnlyInstance> p4 = {1, MovableOnlyInstance(5)};
+  std::pair<const int, MovableOnlyInstance> p5 = {1, MovableOnlyInstance(10)};
+  mmap.insert(std::move(p4));
+  mmap.insert(mmap.find(1), std::move(p5));
+  auto range = mmap.equal_range(1);
+  auto it1 = range.first;
+  ASSERT_NE(it1, range.second);
+  EXPECT_EQ(it1->second.value(), 10);
+  ASSERT_NE(++it1, range.second);
+  EXPECT_EQ(it1->second.value(), 5);
+  EXPECT_EQ(++it1, range.second);
+
+  EXPECT_EQ(tracker.copies(), 0);
+  EXPECT_EQ(tracker.swaps(), 0);
+}
+
+}  // namespace
+
+class BtreeNodePeer {
+ public:
+  // Yields the size of a leaf node with a specific number of values.
+  template <typename ValueType>
+  constexpr static size_t GetTargetNodeSize(size_t target_values_per_node) {
+    return btree_node<
+        set_params<ValueType, std::less<ValueType>, std::allocator<ValueType>,
+                   /*TargetNodeSize=*/256,  // This parameter isn't used here.
+                   /*Multi=*/false>>::SizeWithNValues(target_values_per_node);
+  }
+
+  // Yields the number of values in a (non-root) leaf node for this set.
+  template <typename Set>
+  constexpr static size_t GetNumValuesPerNode() {
+    return btree_node<typename Set::params_type>::kNodeValues;
+  }
+};
+
+namespace {
+
+// A btree set with a specific number of values per node.
+template <typename Key, int TargetValuesPerNode, typename Cmp = std::less<Key>>
+class SizedBtreeSet
+    : public btree_set_container<btree<
+          set_params<Key, Cmp, std::allocator<Key>,
+                     BtreeNodePeer::GetTargetNodeSize<Key>(TargetValuesPerNode),
+                     /*Multi=*/false>>> {
+  using Base = typename SizedBtreeSet::btree_set_container;
+
+ public:
+  SizedBtreeSet() {}
+  using Base::Base;
+};
+
+template <typename Set>
+void ExpectOperationCounts(const int expected_moves,
+                           const int expected_comparisons,
+                           const std::vector<int> &values,
+                           InstanceTracker *tracker, Set *set) {
+  for (const int v : values) set->insert(MovableOnlyInstance(v));
+  set->clear();
+  EXPECT_EQ(tracker->moves(), expected_moves);
+  EXPECT_EQ(tracker->comparisons(), expected_comparisons);
+  EXPECT_EQ(tracker->copies(), 0);
+  EXPECT_EQ(tracker->swaps(), 0);
+  tracker->ResetCopiesMovesSwaps();
+}
+
+// Note: when the values in this test change, it is expected to have an impact
+// on performance.
+TEST(Btree, MovesComparisonsCopiesSwapsTracking) {
+  InstanceTracker tracker;
+  // Note: this is minimum number of values per node.
+  SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/3> set3;
+  // Note: this is the default number of values per node for a set of int32s
+  // (with 64-bit pointers).
+  SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/61> set61;
+  SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/100> set100;
+
+  // Don't depend on flags for random values because then the expectations will
+  // fail if the flags change.
+  std::vector<int> values =
+      GenerateValuesWithSeed<int>(10000, 1 << 22, /*seed=*/23);
+
+  EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set3)>(), 3);
+  EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set61)>(), 61);
+  EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set100)>(), 100);
+  if (sizeof(void *) == 8) {
+    EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<absl::btree_set<int32_t>>(),
+              BtreeNodePeer::GetNumValuesPerNode<decltype(set61)>());
+  }
+
+  // Test key insertion/deletion in random order.
+  ExpectOperationCounts(45281, 132551, values, &tracker, &set3);
+  ExpectOperationCounts(386718, 129807, values, &tracker, &set61);
+  ExpectOperationCounts(586761, 130310, values, &tracker, &set100);
+
+  // Test key insertion/deletion in sorted order.
+  std::sort(values.begin(), values.end());
+  ExpectOperationCounts(26638, 92134, values, &tracker, &set3);
+  ExpectOperationCounts(20208, 87757, values, &tracker, &set61);
+  ExpectOperationCounts(20124, 96583, values, &tracker, &set100);
+
+  // Test key insertion/deletion in reverse sorted order.
+  std::reverse(values.begin(), values.end());
+  ExpectOperationCounts(49951, 119325, values, &tracker, &set3);
+  ExpectOperationCounts(338813, 118266, values, &tracker, &set61);
+  ExpectOperationCounts(534529, 125279, values, &tracker, &set100);
+}
+
+struct MovableOnlyInstanceThreeWayCompare {
+  absl::weak_ordering operator()(const MovableOnlyInstance &a,
+                                 const MovableOnlyInstance &b) const {
+    return a.compare(b);
+  }
+};
+
+// Note: when the values in this test change, it is expected to have an impact
+// on performance.
+TEST(Btree, MovesComparisonsCopiesSwapsTrackingThreeWayCompare) {
+  InstanceTracker tracker;
+  // Note: this is minimum number of values per node.
+  SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/3,
+                MovableOnlyInstanceThreeWayCompare>
+      set3;
+  // Note: this is the default number of values per node for a set of int32s
+  // (with 64-bit pointers).
+  SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/61,
+                MovableOnlyInstanceThreeWayCompare>
+      set61;
+  SizedBtreeSet<MovableOnlyInstance, /*TargetValuesPerNode=*/100,
+                MovableOnlyInstanceThreeWayCompare>
+      set100;
+
+  // Don't depend on flags for random values because then the expectations will
+  // fail if the flags change.
+  std::vector<int> values =
+      GenerateValuesWithSeed<int>(10000, 1 << 22, /*seed=*/23);
+
+  EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set3)>(), 3);
+  EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set61)>(), 61);
+  EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<decltype(set100)>(), 100);
+  if (sizeof(void *) == 8) {
+    EXPECT_EQ(BtreeNodePeer::GetNumValuesPerNode<absl::btree_set<int32_t>>(),
+              BtreeNodePeer::GetNumValuesPerNode<decltype(set61)>());
+  }
+
+  // Test key insertion/deletion in random order.
+  ExpectOperationCounts(45281, 122560, values, &tracker, &set3);
+  ExpectOperationCounts(386718, 119816, values, &tracker, &set61);
+  ExpectOperationCounts(586761, 120319, values, &tracker, &set100);
+
+  // Test key insertion/deletion in sorted order.
+  std::sort(values.begin(), values.end());
+  ExpectOperationCounts(26638, 92134, values, &tracker, &set3);
+  ExpectOperationCounts(20208, 87757, values, &tracker, &set61);
+  ExpectOperationCounts(20124, 96583, values, &tracker, &set100);
+
+  // Test key insertion/deletion in reverse sorted order.
+  std::reverse(values.begin(), values.end());
+  ExpectOperationCounts(49951, 109326, values, &tracker, &set3);
+  ExpectOperationCounts(338813, 108267, values, &tracker, &set61);
+  ExpectOperationCounts(534529, 115280, values, &tracker, &set100);
+}
+
+struct NoDefaultCtor {
+  int num;
+  explicit NoDefaultCtor(int i) : num(i) {}
+
+  friend bool operator<(const NoDefaultCtor& a, const NoDefaultCtor& b) {
+    return a.num < b.num;
+  }
+};
+
+TEST(Btree, BtreeMapCanHoldNoDefaultCtorTypes) {
+  absl::btree_map<NoDefaultCtor, NoDefaultCtor> m;
+
+  for (int i = 1; i <= 99; ++i) {
+    SCOPED_TRACE(i);
+    EXPECT_TRUE(m.emplace(NoDefaultCtor(i), NoDefaultCtor(100 - i)).second);
+  }
+  EXPECT_FALSE(m.emplace(NoDefaultCtor(78), NoDefaultCtor(0)).second);
+
+  auto iter99 = m.find(NoDefaultCtor(99));
+  ASSERT_NE(iter99, m.end());
+  EXPECT_EQ(iter99->second.num, 1);
+
+  auto iter1 = m.find(NoDefaultCtor(1));
+  ASSERT_NE(iter1, m.end());
+  EXPECT_EQ(iter1->second.num, 99);
+
+  auto iter50 = m.find(NoDefaultCtor(50));
+  ASSERT_NE(iter50, m.end());
+  EXPECT_EQ(iter50->second.num, 50);
+
+  auto iter25 = m.find(NoDefaultCtor(25));
+  ASSERT_NE(iter25, m.end());
+  EXPECT_EQ(iter25->second.num, 75);
+}
+
+TEST(Btree, BtreeMultimapCanHoldNoDefaultCtorTypes) {
+  absl::btree_multimap<NoDefaultCtor, NoDefaultCtor> m;
+
+  for (int i = 1; i <= 99; ++i) {
+    SCOPED_TRACE(i);
+    m.emplace(NoDefaultCtor(i), NoDefaultCtor(100 - i));
+  }
+
+  auto iter99 = m.find(NoDefaultCtor(99));
+  ASSERT_NE(iter99, m.end());
+  EXPECT_EQ(iter99->second.num, 1);
+
+  auto iter1 = m.find(NoDefaultCtor(1));
+  ASSERT_NE(iter1, m.end());
+  EXPECT_EQ(iter1->second.num, 99);
+
+  auto iter50 = m.find(NoDefaultCtor(50));
+  ASSERT_NE(iter50, m.end());
+  EXPECT_EQ(iter50->second.num, 50);
+
+  auto iter25 = m.find(NoDefaultCtor(25));
+  ASSERT_NE(iter25, m.end());
+  EXPECT_EQ(iter25->second.num, 75);
+}
+
+TEST(Btree, MapAt) {
+  absl::btree_map<int, int> map = {{1, 2}, {2, 4}};
+  EXPECT_EQ(map.at(1), 2);
+  EXPECT_EQ(map.at(2), 4);
+  map.at(2) = 8;
+  const absl::btree_map<int, int> &const_map = map;
+  EXPECT_EQ(const_map.at(1), 2);
+  EXPECT_EQ(const_map.at(2), 8);
+  try {
+    map.at(3);
+    FAIL() << "Exception not thrown";
+  } catch (const std::out_of_range& e) {
+    EXPECT_STREQ(e.what(), "absl::btree_map::at");
+  }
+}
+
+TEST(Btree, BtreeMultisetEmplace) {
+  const int value_to_insert = 123456;
+  absl::btree_multiset<int> s;
+  auto iter = s.emplace(value_to_insert);
+  ASSERT_NE(iter, s.end());
+  EXPECT_EQ(*iter, value_to_insert);
+  auto iter2 = s.emplace(value_to_insert);
+  EXPECT_NE(iter2, iter);
+  ASSERT_NE(iter2, s.end());
+  EXPECT_EQ(*iter2, value_to_insert);
+  auto result = s.equal_range(value_to_insert);
+  EXPECT_EQ(std::distance(result.first, result.second), 2);
+}
+
+TEST(Btree, BtreeMultisetEmplaceHint) {
+  const int value_to_insert = 123456;
+  absl::btree_multiset<int> s;
+  auto iter = s.emplace(value_to_insert);
+  ASSERT_NE(iter, s.end());
+  EXPECT_EQ(*iter, value_to_insert);
+  auto emplace_iter = s.emplace_hint(iter, value_to_insert);
+  EXPECT_NE(emplace_iter, iter);
+  ASSERT_NE(emplace_iter, s.end());
+  EXPECT_EQ(*emplace_iter, value_to_insert);
+}
+
+TEST(Btree, BtreeMultimapEmplace) {
+  const int key_to_insert = 123456;
+  const char value0[] = "a";
+  absl::btree_multimap<int, std::string> s;
+  auto iter = s.emplace(key_to_insert, value0);
+  ASSERT_NE(iter, s.end());
+  EXPECT_EQ(iter->first, key_to_insert);
+  EXPECT_EQ(iter->second, value0);
+  const char value1[] = "b";
+  auto iter2 = s.emplace(key_to_insert, value1);
+  EXPECT_NE(iter2, iter);
+  ASSERT_NE(iter2, s.end());
+  EXPECT_EQ(iter2->first, key_to_insert);
+  EXPECT_EQ(iter2->second, value1);
+  auto result = s.equal_range(key_to_insert);
+  EXPECT_EQ(std::distance(result.first, result.second), 2);
+}
+
+TEST(Btree, BtreeMultimapEmplaceHint) {
+  const int key_to_insert = 123456;
+  const char value0[] = "a";
+  absl::btree_multimap<int, std::string> s;
+  auto iter = s.emplace(key_to_insert, value0);
+  ASSERT_NE(iter, s.end());
+  EXPECT_EQ(iter->first, key_to_insert);
+  EXPECT_EQ(iter->second, value0);
+  const char value1[] = "b";
+  auto emplace_iter = s.emplace_hint(iter, key_to_insert, value1);
+  EXPECT_NE(emplace_iter, iter);
+  ASSERT_NE(emplace_iter, s.end());
+  EXPECT_EQ(emplace_iter->first, key_to_insert);
+  EXPECT_EQ(emplace_iter->second, value1);
+}
+
+TEST(Btree, ConstIteratorAccessors) {
+  absl::btree_set<int> set;
+  for (int i = 0; i < 100; ++i) {
+    set.insert(i);
+  }
+
+  auto it = set.cbegin();
+  auto r_it = set.crbegin();
+  for (int i = 0; i < 100; ++i, ++it, ++r_it) {
+    ASSERT_EQ(*it, i);
+    ASSERT_EQ(*r_it, 99 - i);
+  }
+  EXPECT_EQ(it, set.cend());
+  EXPECT_EQ(r_it, set.crend());
+}
+
+TEST(Btree, StrSplitCompatible) {
+  const absl::btree_set<std::string> split_set = absl::StrSplit("a,b,c", ',');
+  const absl::btree_set<std::string> expected_set = {"a", "b", "c"};
+
+  EXPECT_EQ(split_set, expected_set);
+}
+
+// We can't use EXPECT_EQ/etc. to compare absl::weak_ordering because they
+// convert literal 0 to int and absl::weak_ordering can only be compared with
+// literal 0. Defining this function allows for avoiding ClangTidy warnings.
+bool Identity(const bool b) { return b; }
+
+TEST(Btree, ValueComp) {
+  absl::btree_set<int> s;
+  EXPECT_TRUE(s.value_comp()(1, 2));
+  EXPECT_FALSE(s.value_comp()(2, 2));
+  EXPECT_FALSE(s.value_comp()(2, 1));
+
+  absl::btree_map<int, int> m1;
+  EXPECT_TRUE(m1.value_comp()(std::make_pair(1, 0), std::make_pair(2, 0)));
+  EXPECT_FALSE(m1.value_comp()(std::make_pair(2, 0), std::make_pair(2, 0)));
+  EXPECT_FALSE(m1.value_comp()(std::make_pair(2, 0), std::make_pair(1, 0)));
+
+  absl::btree_map<std::string, int> m2;
+  EXPECT_TRUE(Identity(
+      m2.value_comp()(std::make_pair("a", 0), std::make_pair("b", 0)) < 0));
+  EXPECT_TRUE(Identity(
+      m2.value_comp()(std::make_pair("b", 0), std::make_pair("b", 0)) == 0));
+  EXPECT_TRUE(Identity(
+      m2.value_comp()(std::make_pair("b", 0), std::make_pair("a", 0)) > 0));
+}
+
+TEST(Btree, DefaultConstruction) {
+  absl::btree_set<int> s;
+  absl::btree_map<int, int> m;
+  absl::btree_multiset<int> ms;
+  absl::btree_multimap<int, int> mm;
+
+  EXPECT_TRUE(s.empty());
+  EXPECT_TRUE(m.empty());
+  EXPECT_TRUE(ms.empty());
+  EXPECT_TRUE(mm.empty());
+}
+
+TEST(Btree, SwissTableHashable) {
+  static constexpr int kValues = 10000;
+  std::vector<int> values(kValues);
+  std::iota(values.begin(), values.end(), 0);
+  std::vector<std::pair<int, int>> map_values;
+  for (int v : values) map_values.emplace_back(v, -v);
+
+  using set = absl::btree_set<int>;
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly({
+      set{},
+      set{1},
+      set{2},
+      set{1, 2},
+      set{2, 1},
+      set(values.begin(), values.end()),
+      set(values.rbegin(), values.rend()),
+  }));
+
+  using mset = absl::btree_multiset<int>;
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly({
+      mset{},
+      mset{1},
+      mset{1, 1},
+      mset{2},
+      mset{2, 2},
+      mset{1, 2},
+      mset{1, 1, 2},
+      mset{1, 2, 2},
+      mset{1, 1, 2, 2},
+      mset(values.begin(), values.end()),
+      mset(values.rbegin(), values.rend()),
+  }));
+
+  using map = absl::btree_map<int, int>;
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly({
+      map{},
+      map{{1, 0}},
+      map{{1, 1}},
+      map{{2, 0}},
+      map{{2, 2}},
+      map{{1, 0}, {2, 1}},
+      map(map_values.begin(), map_values.end()),
+      map(map_values.rbegin(), map_values.rend()),
+  }));
+
+  using mmap = absl::btree_multimap<int, int>;
+  EXPECT_TRUE(absl::VerifyTypeImplementsAbslHashCorrectly({
+      mmap{},
+      mmap{{1, 0}},
+      mmap{{1, 1}},
+      mmap{{1, 0}, {1, 1}},
+      mmap{{1, 1}, {1, 0}},
+      mmap{{2, 0}},
+      mmap{{2, 2}},
+      mmap{{1, 0}, {2, 1}},
+      mmap(map_values.begin(), map_values.end()),
+      mmap(map_values.rbegin(), map_values.rend()),
+  }));
+}
+
+TEST(Btree, ComparableSet) {
+  absl::btree_set<int> s1 = {1, 2};
+  absl::btree_set<int> s2 = {2, 3};
+  EXPECT_LT(s1, s2);
+  EXPECT_LE(s1, s2);
+  EXPECT_LE(s1, s1);
+  EXPECT_GT(s2, s1);
+  EXPECT_GE(s2, s1);
+  EXPECT_GE(s1, s1);
+}
+
+TEST(Btree, ComparableSetsDifferentLength) {
+  absl::btree_set<int> s1 = {1, 2};
+  absl::btree_set<int> s2 = {1, 2, 3};
+  EXPECT_LT(s1, s2);
+  EXPECT_LE(s1, s2);
+  EXPECT_GT(s2, s1);
+  EXPECT_GE(s2, s1);
+}
+
+TEST(Btree, ComparableMultiset) {
+  absl::btree_multiset<int> s1 = {1, 2};
+  absl::btree_multiset<int> s2 = {2, 3};
+  EXPECT_LT(s1, s2);
+  EXPECT_LE(s1, s2);
+  EXPECT_LE(s1, s1);
+  EXPECT_GT(s2, s1);
+  EXPECT_GE(s2, s1);
+  EXPECT_GE(s1, s1);
+}
+
+TEST(Btree, ComparableMap) {
+  absl::btree_map<int, int> s1 = {{1, 2}};
+  absl::btree_map<int, int> s2 = {{2, 3}};
+  EXPECT_LT(s1, s2);
+  EXPECT_LE(s1, s2);
+  EXPECT_LE(s1, s1);
+  EXPECT_GT(s2, s1);
+  EXPECT_GE(s2, s1);
+  EXPECT_GE(s1, s1);
+}
+
+TEST(Btree, ComparableMultimap) {
+  absl::btree_multimap<int, int> s1 = {{1, 2}};
+  absl::btree_multimap<int, int> s2 = {{2, 3}};
+  EXPECT_LT(s1, s2);
+  EXPECT_LE(s1, s2);
+  EXPECT_LE(s1, s1);
+  EXPECT_GT(s2, s1);
+  EXPECT_GE(s2, s1);
+  EXPECT_GE(s1, s1);
+}
+
+TEST(Btree, ComparableSetWithCustomComparator) {
+  // As specified by
+  // http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3337.pdf section
+  // [container.requirements.general].12, ordering associative containers always
+  // uses default '<' operator
+  // - even if otherwise the container uses custom functor.
+  absl::btree_set<int, std::greater<int>> s1 = {1, 2};
+  absl::btree_set<int, std::greater<int>> s2 = {2, 3};
+  EXPECT_LT(s1, s2);
+  EXPECT_LE(s1, s2);
+  EXPECT_LE(s1, s1);
+  EXPECT_GT(s2, s1);
+  EXPECT_GE(s2, s1);
+  EXPECT_GE(s1, s1);
+}
+
+TEST(Btree, EraseReturnsIterator) {
+  absl::btree_set<int> set = {1, 2, 3, 4, 5};
+  auto result_it = set.erase(set.begin(), set.find(3));
+  EXPECT_EQ(result_it, set.find(3));
+  result_it = set.erase(set.find(5));
+  EXPECT_EQ(result_it, set.end());
+}
+
+TEST(Btree, ExtractAndInsertNodeHandleSet) {
+  absl::btree_set<int> src1 = {1, 2, 3, 4, 5};
+  auto nh = src1.extract(src1.find(3));
+  EXPECT_THAT(src1, ElementsAre(1, 2, 4, 5));
+  absl::btree_set<int> other;
+  absl::btree_set<int>::insert_return_type res = other.insert(std::move(nh));
+  EXPECT_THAT(other, ElementsAre(3));
+  EXPECT_EQ(res.position, other.find(3));
+  EXPECT_TRUE(res.inserted);
+  EXPECT_TRUE(res.node.empty());
+
+  absl::btree_set<int> src2 = {3, 4};
+  nh = src2.extract(src2.find(3));
+  EXPECT_THAT(src2, ElementsAre(4));
+  res = other.insert(std::move(nh));
+  EXPECT_THAT(other, ElementsAre(3));
+  EXPECT_EQ(res.position, other.find(3));
+  EXPECT_FALSE(res.inserted);
+  ASSERT_FALSE(res.node.empty());
+  EXPECT_EQ(res.node.value(), 3);
+}
+
+struct Deref {
+  bool operator()(const std::unique_ptr<int> &lhs,
+                  const std::unique_ptr<int> &rhs) const {
+    return *lhs < *rhs;
+  }
+};
+
+TEST(Btree, ExtractWithUniquePtr) {
+  absl::btree_set<std::unique_ptr<int>, Deref> s;
+  s.insert(absl::make_unique<int>(1));
+  s.insert(absl::make_unique<int>(2));
+  s.insert(absl::make_unique<int>(3));
+  s.insert(absl::make_unique<int>(4));
+  s.insert(absl::make_unique<int>(5));
+  auto nh = s.extract(s.find(absl::make_unique<int>(3)));
+  EXPECT_EQ(s.size(), 4);
+  EXPECT_EQ(*nh.value(), 3);
+  s.insert(std::move(nh));
+  EXPECT_EQ(s.size(), 5);
+}
+
+TEST(Btree, ExtractAndInsertNodeHandleMultiSet) {
+  absl::btree_multiset<int> src1 = {1, 2, 3, 3, 4, 5};
+  auto nh = src1.extract(src1.find(3));
+  EXPECT_THAT(src1, ElementsAre(1, 2, 3, 4, 5));
+  absl::btree_multiset<int> other;
+  auto res = other.insert(std::move(nh));
+  EXPECT_THAT(other, ElementsAre(3));
+  EXPECT_EQ(res, other.find(3));
+
+  absl::btree_multiset<int> src2 = {3, 4};
+  nh = src2.extract(src2.find(3));
+  EXPECT_THAT(src2, ElementsAre(4));
+  res = other.insert(std::move(nh));
+  EXPECT_THAT(other, ElementsAre(3, 3));
+  EXPECT_EQ(res, ++other.find(3));
+}
+
+TEST(Btree, ExtractAndInsertNodeHandleMap) {
+  absl::btree_map<int, int> src1 = {{1, 2}, {3, 4}, {5, 6}};
+  auto nh = src1.extract(src1.find(3));
+  EXPECT_THAT(src1, ElementsAre(Pair(1, 2), Pair(5, 6)));
+  absl::btree_map<int, int> other;
+  absl::btree_map<int, int>::insert_return_type res =
+      other.insert(std::move(nh));
+  EXPECT_THAT(other, ElementsAre(Pair(3, 4)));
+  EXPECT_EQ(res.position, other.find(3));
+  EXPECT_TRUE(res.inserted);
+  EXPECT_TRUE(res.node.empty());
+
+  absl::btree_map<int, int> src2 = {{3, 6}};
+  nh = src2.extract(src2.find(3));
+  EXPECT_TRUE(src2.empty());
+  res = other.insert(std::move(nh));
+  EXPECT_THAT(other, ElementsAre(Pair(3, 4)));
+  EXPECT_EQ(res.position, other.find(3));
+  EXPECT_FALSE(res.inserted);
+  ASSERT_FALSE(res.node.empty());
+  EXPECT_EQ(res.node.key(), 3);
+  EXPECT_EQ(res.node.mapped(), 6);
+}
+
+TEST(Btree, ExtractAndInsertNodeHandleMultiMap) {
+  absl::btree_multimap<int, int> src1 = {{1, 2}, {3, 4}, {5, 6}};
+  auto nh = src1.extract(src1.find(3));
+  EXPECT_THAT(src1, ElementsAre(Pair(1, 2), Pair(5, 6)));
+  absl::btree_multimap<int, int> other;
+  auto res = other.insert(std::move(nh));
+  EXPECT_THAT(other, ElementsAre(Pair(3, 4)));
+  EXPECT_EQ(res, other.find(3));
+
+  absl::btree_multimap<int, int> src2 = {{3, 6}};
+  nh = src2.extract(src2.find(3));
+  EXPECT_TRUE(src2.empty());
+  res = other.insert(std::move(nh));
+  EXPECT_THAT(other, ElementsAre(Pair(3, 4), Pair(3, 6)));
+  EXPECT_EQ(res, ++other.begin());
+}
+
+// For multisets, insert with hint also affects correctness because we need to
+// insert immediately before the hint if possible.
+struct InsertMultiHintData {
+  int key;
+  int not_key;
+  bool operator==(const InsertMultiHintData other) const {
+    return key == other.key && not_key == other.not_key;
+  }
+};
+
+struct InsertMultiHintDataKeyCompare {
+  using is_transparent = void;
+  bool operator()(const InsertMultiHintData a,
+                  const InsertMultiHintData b) const {
+    return a.key < b.key;
+  }
+  bool operator()(const int a, const InsertMultiHintData b) const {
+    return a < b.key;
+  }
+  bool operator()(const InsertMultiHintData a, const int b) const {
+    return a.key < b;
+  }
+};
+
+TEST(Btree, InsertHintNodeHandle) {
+  // For unique sets, insert with hint is just a performance optimization.
+  // Test that insert works correctly when the hint is right or wrong.
+  {
+    absl::btree_set<int> src = {1, 2, 3, 4, 5};
+    auto nh = src.extract(src.find(3));
+    EXPECT_THAT(src, ElementsAre(1, 2, 4, 5));
+    absl::btree_set<int> other = {0, 100};
+    // Test a correct hint.
+    auto it = other.insert(other.lower_bound(3), std::move(nh));
+    EXPECT_THAT(other, ElementsAre(0, 3, 100));
+    EXPECT_EQ(it, other.find(3));
+
+    nh = src.extract(src.find(5));
+    // Test an incorrect hint.
+    it = other.insert(other.end(), std::move(nh));
+    EXPECT_THAT(other, ElementsAre(0, 3, 5, 100));
+    EXPECT_EQ(it, other.find(5));
+  }
+
+  absl::btree_multiset<InsertMultiHintData, InsertMultiHintDataKeyCompare> src =
+      {{1, 2}, {3, 4}, {3, 5}};
+  auto nh = src.extract(src.lower_bound(3));
+  EXPECT_EQ(nh.value(), (InsertMultiHintData{3, 4}));
+  absl::btree_multiset<InsertMultiHintData, InsertMultiHintDataKeyCompare>
+      other = {{3, 1}, {3, 2}, {3, 3}};
+  auto it = other.insert(--other.end(), std::move(nh));
+  EXPECT_THAT(
+      other, ElementsAre(InsertMultiHintData{3, 1}, InsertMultiHintData{3, 2},
+                         InsertMultiHintData{3, 4}, InsertMultiHintData{3, 3}));
+  EXPECT_EQ(it, --(--other.end()));
+
+  nh = src.extract(src.find(3));
+  EXPECT_EQ(nh.value(), (InsertMultiHintData{3, 5}));
+  it = other.insert(other.begin(), std::move(nh));
+  EXPECT_THAT(other,
+              ElementsAre(InsertMultiHintData{3, 5}, InsertMultiHintData{3, 1},
+                          InsertMultiHintData{3, 2}, InsertMultiHintData{3, 4},
+                          InsertMultiHintData{3, 3}));
+  EXPECT_EQ(it, other.begin());
+}
+
+struct IntCompareToCmp {
+  absl::weak_ordering operator()(int a, int b) const {
+    if (a < b) return absl::weak_ordering::less;
+    if (a > b) return absl::weak_ordering::greater;
+    return absl::weak_ordering::equivalent;
+  }
+};
+
+TEST(Btree, MergeIntoUniqueContainers) {
+  absl::btree_set<int, IntCompareToCmp> src1 = {1, 2, 3};
+  absl::btree_multiset<int> src2 = {3, 4, 4, 5};
+  absl::btree_set<int> dst;
+
+  dst.merge(src1);
+  EXPECT_TRUE(src1.empty());
+  EXPECT_THAT(dst, ElementsAre(1, 2, 3));
+  dst.merge(src2);
+  EXPECT_THAT(src2, ElementsAre(3, 4));
+  EXPECT_THAT(dst, ElementsAre(1, 2, 3, 4, 5));
+}
+
+TEST(Btree, MergeIntoUniqueContainersWithCompareTo) {
+  absl::btree_set<int, IntCompareToCmp> src1 = {1, 2, 3};
+  absl::btree_multiset<int> src2 = {3, 4, 4, 5};
+  absl::btree_set<int, IntCompareToCmp> dst;
+
+  dst.merge(src1);
+  EXPECT_TRUE(src1.empty());
+  EXPECT_THAT(dst, ElementsAre(1, 2, 3));
+  dst.merge(src2);
+  EXPECT_THAT(src2, ElementsAre(3, 4));
+  EXPECT_THAT(dst, ElementsAre(1, 2, 3, 4, 5));
+}
+
+TEST(Btree, MergeIntoMultiContainers) {
+  absl::btree_set<int, IntCompareToCmp> src1 = {1, 2, 3};
+  absl::btree_multiset<int> src2 = {3, 4, 4, 5};
+  absl::btree_multiset<int> dst;
+
+  dst.merge(src1);
+  EXPECT_TRUE(src1.empty());
+  EXPECT_THAT(dst, ElementsAre(1, 2, 3));
+  dst.merge(src2);
+  EXPECT_TRUE(src2.empty());
+  EXPECT_THAT(dst, ElementsAre(1, 2, 3, 3, 4, 4, 5));
+}
+
+TEST(Btree, MergeIntoMultiContainersWithCompareTo) {
+  absl::btree_set<int, IntCompareToCmp> src1 = {1, 2, 3};
+  absl::btree_multiset<int> src2 = {3, 4, 4, 5};
+  absl::btree_multiset<int, IntCompareToCmp> dst;
+
+  dst.merge(src1);
+  EXPECT_TRUE(src1.empty());
+  EXPECT_THAT(dst, ElementsAre(1, 2, 3));
+  dst.merge(src2);
+  EXPECT_TRUE(src2.empty());
+  EXPECT_THAT(dst, ElementsAre(1, 2, 3, 3, 4, 4, 5));
+}
+
+TEST(Btree, MergeIntoMultiMapsWithDifferentComparators) {
+  absl::btree_map<int, int, IntCompareToCmp> src1 = {{1, 1}, {2, 2}, {3, 3}};
+  absl::btree_multimap<int, int, std::greater<int>> src2 = {
+      {5, 5}, {4, 1}, {4, 4}, {3, 2}};
+  absl::btree_multimap<int, int> dst;
+
+  dst.merge(src1);
+  EXPECT_TRUE(src1.empty());
+  EXPECT_THAT(dst, ElementsAre(Pair(1, 1), Pair(2, 2), Pair(3, 3)));
+  dst.merge(src2);
+  EXPECT_TRUE(src2.empty());
+  EXPECT_THAT(dst, ElementsAre(Pair(1, 1), Pair(2, 2), Pair(3, 3), Pair(3, 2),
+                               Pair(4, 1), Pair(4, 4), Pair(5, 5)));
+}
+
+struct KeyCompareToWeakOrdering {
+  template <typename T>
+  absl::weak_ordering operator()(const T &a, const T &b) const {
+    return a < b ? absl::weak_ordering::less
+                 : a == b ? absl::weak_ordering::equivalent
+                          : absl::weak_ordering::greater;
+  }
+};
+
+struct KeyCompareToStrongOrdering {
+  template <typename T>
+  absl::strong_ordering operator()(const T &a, const T &b) const {
+    return a < b ? absl::strong_ordering::less
+                 : a == b ? absl::strong_ordering::equal
+                          : absl::strong_ordering::greater;
+  }
+};
+
+TEST(Btree, UserProvidedKeyCompareToComparators) {
+  absl::btree_set<int, KeyCompareToWeakOrdering> weak_set = {1, 2, 3};
+  EXPECT_TRUE(weak_set.contains(2));
+  EXPECT_FALSE(weak_set.contains(4));
+
+  absl::btree_set<int, KeyCompareToStrongOrdering> strong_set = {1, 2, 3};
+  EXPECT_TRUE(strong_set.contains(2));
+  EXPECT_FALSE(strong_set.contains(4));
+}
+
+TEST(Btree, TryEmplaceBasicTest) {
+  absl::btree_map<int, std::string> m;
+
+  // Should construct a std::string from the literal.
+  m.try_emplace(1, "one");
+  EXPECT_EQ(1, m.size());
+
+  // Try other std::string constructors and const lvalue key.
+  const int key(42);
+  m.try_emplace(key, 3, 'a');
+  m.try_emplace(2, std::string("two"));
+
+  EXPECT_TRUE(std::is_sorted(m.begin(), m.end()));
+  EXPECT_THAT(m, ElementsAreArray(std::vector<std::pair<int, std::string>>{
+                     {1, "one"}, {2, "two"}, {42, "aaa"}}));
+}
+
+TEST(Btree, TryEmplaceWithHintWorks) {
+  // Use a counting comparator here to verify that hint is used.
+  int calls = 0;
+  auto cmp = [&calls](int x, int y) {
+    ++calls;
+    return x < y;
+  };
+  using Cmp = decltype(cmp);
+
+  absl::btree_map<int, int, Cmp> m(cmp);
+  for (int i = 0; i < 128; ++i) {
+    m.emplace(i, i);
+  }
+
+  // Sanity check for the comparator
+  calls = 0;
+  m.emplace(127, 127);
+  EXPECT_GE(calls, 4);
+
+  // Try with begin hint:
+  calls = 0;
+  auto it = m.try_emplace(m.begin(), -1, -1);
+  EXPECT_EQ(129, m.size());
+  EXPECT_EQ(it, m.begin());
+  EXPECT_LE(calls, 2);
+
+  // Try with end hint:
+  calls = 0;
+  std::pair<int, int> pair1024 = {1024, 1024};
+  it = m.try_emplace(m.end(), pair1024.first, pair1024.second);
+  EXPECT_EQ(130, m.size());
+  EXPECT_EQ(it, --m.end());
+  EXPECT_LE(calls, 2);
+
+  // Try value already present, bad hint; ensure no duplicate added:
+  calls = 0;
+  it = m.try_emplace(m.end(), 16, 17);
+  EXPECT_EQ(130, m.size());
+  EXPECT_GE(calls, 4);
+  EXPECT_EQ(it, m.find(16));
+
+  // Try value already present, hint points directly to it:
+  calls = 0;
+  it = m.try_emplace(it, 16, 17);
+  EXPECT_EQ(130, m.size());
+  EXPECT_LE(calls, 2);
+  EXPECT_EQ(it, m.find(16));
+
+  m.erase(2);
+  EXPECT_EQ(129, m.size());
+  auto hint = m.find(3);
+  // Try emplace in the middle of two other elements.
+  calls = 0;
+  m.try_emplace(hint, 2, 2);
+  EXPECT_EQ(130, m.size());
+  EXPECT_LE(calls, 2);
+
+  EXPECT_TRUE(std::is_sorted(m.begin(), m.end()));
+}
+
+TEST(Btree, TryEmplaceWithBadHint) {
+  absl::btree_map<int, int> m = {{1, 1}, {9, 9}};
+
+  // Bad hint (too small), should still emplace:
+  auto it = m.try_emplace(m.begin(), 2, 2);
+  EXPECT_EQ(it, ++m.begin());
+  EXPECT_THAT(m, ElementsAreArray(
+                     std::vector<std::pair<int, int>>{{1, 1}, {2, 2}, {9, 9}}));
+
+  // Bad hint, too large this time:
+  it = m.try_emplace(++(++m.begin()), 0, 0);
+  EXPECT_EQ(it, m.begin());
+  EXPECT_THAT(m, ElementsAreArray(std::vector<std::pair<int, int>>{
+                     {0, 0}, {1, 1}, {2, 2}, {9, 9}}));
+}
+
+TEST(Btree, TryEmplaceMaintainsSortedOrder) {
+  absl::btree_map<int, std::string> m;
+  std::pair<int, std::string> pair5 = {5, "five"};
+
+  // Test both lvalue & rvalue emplace.
+  m.try_emplace(10, "ten");
+  m.try_emplace(pair5.first, pair5.second);
+  EXPECT_EQ(2, m.size());
+  EXPECT_TRUE(std::is_sorted(m.begin(), m.end()));
+
+  int int100{100};
+  m.try_emplace(int100, "hundred");
+  m.try_emplace(1, "one");
+  EXPECT_EQ(4, m.size());
+  EXPECT_TRUE(std::is_sorted(m.begin(), m.end()));
+}
+
+TEST(Btree, TryEmplaceWithHintAndNoValueArgsWorks) {
+  absl::btree_map<int, int> m;
+  m.try_emplace(m.end(), 1);
+  EXPECT_EQ(0, m[1]);
+}
+
+TEST(Btree, TryEmplaceWithHintAndMultipleValueArgsWorks) {
+  absl::btree_map<int, std::string> m;
+  m.try_emplace(m.end(), 1, 10, 'a');
+  EXPECT_EQ(std::string(10, 'a'), m[1]);
+}
+
+TEST(Btree, MoveAssignmentAllocatorPropagation) {
+  InstanceTracker tracker;
+
+  int64_t bytes1 = 0, bytes2 = 0;
+  PropagatingCountingAlloc<MovableOnlyInstance> allocator1(&bytes1);
+  PropagatingCountingAlloc<MovableOnlyInstance> allocator2(&bytes2);
+  std::less<MovableOnlyInstance> cmp;
+
+  // Test propagating allocator_type.
+  {
+    absl::btree_set<MovableOnlyInstance, std::less<MovableOnlyInstance>,
+                    PropagatingCountingAlloc<MovableOnlyInstance>>
+        set1(cmp, allocator1), set2(cmp, allocator2);
+
+    for (int i = 0; i < 100; ++i) set1.insert(MovableOnlyInstance(i));
+
+    tracker.ResetCopiesMovesSwaps();
+    set2 = std::move(set1);
+    EXPECT_EQ(tracker.moves(), 0);
+  }
+  // Test non-propagating allocator_type with equal allocators.
+  {
+    absl::btree_set<MovableOnlyInstance, std::less<MovableOnlyInstance>,
+                    CountingAllocator<MovableOnlyInstance>>
+        set1(cmp, allocator1), set2(cmp, allocator1);
+
+    for (int i = 0; i < 100; ++i) set1.insert(MovableOnlyInstance(i));
+
+    tracker.ResetCopiesMovesSwaps();
+    set2 = std::move(set1);
+    EXPECT_EQ(tracker.moves(), 0);
+  }
+  // Test non-propagating allocator_type with different allocators.
+  {
+    absl::btree_set<MovableOnlyInstance, std::less<MovableOnlyInstance>,
+                    CountingAllocator<MovableOnlyInstance>>
+        set1(cmp, allocator1), set2(cmp, allocator2);
+
+    for (int i = 0; i < 100; ++i) set1.insert(MovableOnlyInstance(i));
+
+    tracker.ResetCopiesMovesSwaps();
+    set2 = std::move(set1);
+    EXPECT_GE(tracker.moves(), 100);
+  }
+}
+
+}  // namespace
+}  // namespace container_internal
+}  // namespace absl