Changes imported from Abseil "staging" branch:

  - 55c7dd8ad1570b4e6ce2103ed4d4b6becdea0d96 Remove line continuations which require CMake >= 3.0.  Al... by Jon Cohen <cohenjon@google.com>
  - ee66ad72a90259d6286bbfea7241ed976bb0f6fb Change absl::ParseDuration() to avoid double.  This allow... by Abseil Team <absl-team@google.com>
  - 89cf4cd49d8ff25cb3d29f06b2090029a2024e89 Internal change by Gennadiy Rozental <rogeeff@google.com>
  - cdb5879bf6aaf6bbd2ad1fe4a2b144bbdf0389c7 Internal change by Gennadiy Rozental <rogeeff@google.com>
  - e7b29d11bf24a63bf7637689ada8be7d619844fc Internal change by Gennadiy Rozental <rogeeff@google.com>
  - 2d4fc08d5d64a7760ad6230eccdb5b8014c2b0c3 Update the exception-safety testing framework. by Jon Cohen <cohenjon@google.com>

GitOrigin-RevId: 55c7dd8ad1570b4e6ce2103ed4d4b6becdea0d96
Change-Id: I6b560cbc4570dfc5aa9a2f90e84d69904df7eac5

4 files changed, 280 insertions, 95 deletions

diff --git a/absl/base/BUILD.bazel b/absl/base/BUILD.bazel
index 64057f6c9816..e528463345b8 100644
--- a/absl/base/BUILD.bazel
+++ b/absl/base/BUILD.bazel
@@ -238,6 +238,7 @@ cc_library(
     deps = [
         ":config",
         ":pretty_function",
+        "//absl/memory",
         "//absl/meta:type_traits",
         "//absl/strings",
         "@com_google_googletest//:gtest",
diff --git a/absl/base/exception_safety_testing_test.cc b/absl/base/exception_safety_testing_test.cc
index 365732c6721a..c1b5df265467 100644
--- a/absl/base/exception_safety_testing_test.cc
+++ b/absl/base/exception_safety_testing_test.cc
@@ -14,10 +14,6 @@ namespace absl {
 namespace {
 using ::absl::exceptions_internal::TestException;
 
-void SetCountdown() { exceptions_internal::countdown = 0; }
-
-void UnsetCountdown() { exceptions_internal::countdown = -1; }
-
 // EXPECT_NO_THROW can't inspect the thrown inspection in general.
 template <typename F>
 void ExpectNoThrow(const F& f) {
@@ -395,12 +391,15 @@ struct FailsBasicGuarantee {
     ++i;
   }
 
-  bool operator!=(const FailsBasicGuarantee& other) const {
+  bool operator==(const FailsBasicGuarantee& other) const {
     return i != other.i;
   }
 
-  friend bool AbslCheckInvariants(const FailsBasicGuarantee& g) {
-    return g.i >= 0;
+  friend testing::AssertionResult AbslCheckInvariants(
+      const FailsBasicGuarantee& g) {
+    if (g.i >= 0) return testing::AssertionSuccess();
+    return testing::AssertionFailure()
+           << "i should be non-negative but is " << g.i;
   }
 
   int i = 0;
@@ -408,7 +407,7 @@ struct FailsBasicGuarantee {
 
 TEST(ExceptionCheckTest, BasicGuaranteeFailure) {
   FailsBasicGuarantee g;
-  EXPECT_FALSE(TestBasicGuarantee(&g, CallOperator{}));
+  EXPECT_FALSE(TestExceptionSafety(&g, CallOperator{}));
 }
 
 struct FollowsBasicGuarantee {
@@ -417,12 +416,15 @@ struct FollowsBasicGuarantee {
     ThrowingValue<> bomb;
   }
 
-  bool operator!=(const FollowsBasicGuarantee& other) const {
-    return i != other.i;
+  bool operator==(const FollowsBasicGuarantee& other) const {
+    return i == other.i;
   }
 
-  friend bool AbslCheckInvariants(const FollowsBasicGuarantee& g) {
-    return g.i >= 0;
+  friend testing::AssertionResult AbslCheckInvariants(
+      const FollowsBasicGuarantee& g) {
+    if (g.i >= 0) return testing::AssertionSuccess();
+    return testing::AssertionFailure()
+           << "i should be non-negative but is " << g.i;
   }
 
   int i = 0;
@@ -430,30 +432,79 @@ struct FollowsBasicGuarantee {
 
 TEST(ExceptionCheckTest, BasicGuarantee) {
   FollowsBasicGuarantee g;
-  EXPECT_TRUE(TestBasicGuarantee(&g, CallOperator{}));
+  EXPECT_TRUE(TestExceptionSafety(&g, CallOperator{}));
 }
 
 TEST(ExceptionCheckTest, StrongGuaranteeFailure) {
   {
     FailsBasicGuarantee g;
-    EXPECT_FALSE(TestStrongGuarantee(&g, CallOperator{}));
+    EXPECT_FALSE(TestExceptionSafety(&g, CallOperator{}, StrongGuarantee(g)));
   }
 
   {
     FollowsBasicGuarantee g;
-    EXPECT_FALSE(TestStrongGuarantee(&g, CallOperator{}));
+    EXPECT_FALSE(TestExceptionSafety(&g, CallOperator{}, StrongGuarantee(g)));
+  }
+}
+
+struct BasicGuaranteeWithExtraInvariants {
+  // After operator(), i is incremented.  If operator() throws, i is set to 9999
+  void operator()() {
+    int old_i = i;
+    i = kExceptionSentinel;
+    ThrowingValue<> bomb;
+    i = ++old_i;
+  }
+
+  bool operator==(const FollowsBasicGuarantee& other) const {
+    return i == other.i;
+  }
+
+  friend testing::AssertionResult AbslCheckInvariants(
+      const BasicGuaranteeWithExtraInvariants& g) {
+    if (g.i >= 0) return testing::AssertionSuccess();
+    return testing::AssertionFailure()
+           << "i should be non-negative but is " << g.i;
+  }
+
+  int i = 0;
+  static constexpr int kExceptionSentinel = 9999;
+};
+constexpr int BasicGuaranteeWithExtraInvariants::kExceptionSentinel;
+
+TEST(ExceptionCheckTest, BasicGuaranteeWithInvariants) {
+  {
+    BasicGuaranteeWithExtraInvariants g;
+    EXPECT_TRUE(TestExceptionSafety(&g, CallOperator{}));
+  }
+
+  {
+    BasicGuaranteeWithExtraInvariants g;
+    EXPECT_TRUE(TestExceptionSafety(
+        &g, CallOperator{}, [](const BasicGuaranteeWithExtraInvariants& w) {
+          if (w.i == BasicGuaranteeWithExtraInvariants::kExceptionSentinel) {
+            return testing::AssertionSuccess();
+          }
+          return testing::AssertionFailure()
+                 << "i should be "
+                 << BasicGuaranteeWithExtraInvariants::kExceptionSentinel
+                 << ", but is " << w.i;
+        }));
   }
 }
 
 struct FollowsStrongGuarantee {
   void operator()() { ThrowingValue<> bomb; }
 
-  bool operator!=(const FollowsStrongGuarantee& other) const {
-    return i != other.i;
+  bool operator==(const FollowsStrongGuarantee& other) const {
+    return i == other.i;
   }
 
-  friend bool AbslCheckInvariants(const FollowsStrongGuarantee& g) {
-    return g.i >= 0;
+  friend testing::AssertionResult AbslCheckInvariants(
+      const FollowsStrongGuarantee& g) {
+    if (g.i >= 0) return testing::AssertionSuccess();
+    return testing::AssertionFailure()
+           << "i should be non-negative but is " << g.i;
   }
 
   int i = 0;
@@ -461,8 +512,65 @@ struct FollowsStrongGuarantee {
 
 TEST(ExceptionCheckTest, StrongGuarantee) {
   FollowsStrongGuarantee g;
-  EXPECT_TRUE(TestBasicGuarantee(&g, CallOperator{}));
-  EXPECT_TRUE(TestStrongGuarantee(&g, CallOperator{}));
+  EXPECT_TRUE(TestExceptionSafety(&g, CallOperator{}));
+  EXPECT_TRUE(TestExceptionSafety(&g, CallOperator{}, StrongGuarantee(g)));
+}
+
+struct NonCopyable {
+  NonCopyable(const NonCopyable&) = delete;
+  explicit NonCopyable(int ii) : i(ii) {}
+
+  void operator()() { ThrowingValue<> bomb; }
+
+  bool operator==(const NonCopyable& other) const { return i == other.i; }
+
+  friend testing::AssertionResult AbslCheckInvariants(const NonCopyable& g) {
+    if (g.i >= 0) return testing::AssertionSuccess();
+    return testing::AssertionFailure()
+           << "i should be non-negative but is " << g.i;
+  }
+
+  int i;
+};
+
+TEST(ExceptionCheckTest, NonCopyable) {
+  NonCopyable g(0);
+  EXPECT_TRUE(TestExceptionSafety(&g, CallOperator{}));
+  EXPECT_TRUE(TestExceptionSafety(
+      &g, CallOperator{},
+      PointeeStrongGuarantee(absl::make_unique<NonCopyable>(g.i))));
+}
+
+struct NonEqualityComparable {
+  void operator()() { ThrowingValue<> bomb; }
+
+  void ModifyOnThrow() {
+    ++i;
+    ThrowingValue<> bomb;
+    static_cast<void>(bomb);
+    --i;
+  }
+
+  friend testing::AssertionResult AbslCheckInvariants(
+      const NonEqualityComparable& g) {
+    if (g.i >= 0) return testing::AssertionSuccess();
+    return testing::AssertionFailure()
+           << "i should be non-negative but is " << g.i;
+  }
+
+  int i = 0;
+};
+
+TEST(ExceptionCheckTest, NonEqualityComparable) {
+  NonEqualityComparable g;
+  auto comp = [](const NonEqualityComparable& a,
+                 const NonEqualityComparable& b) { return a.i == b.i; };
+  EXPECT_TRUE(TestExceptionSafety(&g, CallOperator{}));
+  EXPECT_TRUE(
+      TestExceptionSafety(&g, CallOperator{}, absl::StrongGuarantee(g, comp)));
+  EXPECT_FALSE(TestExceptionSafety(
+      &g, [&](NonEqualityComparable* n) { n->ModifyOnThrow(); },
+      absl::StrongGuarantee(g, comp)));
 }
 
 template <typename T>
@@ -480,11 +588,14 @@ struct InstructionCounter {
     ++counter;
   }
 
-  bool operator!=(const InstructionCounter<ThrowingValue<>>& other) const {
-    return false;
+  bool operator==(const InstructionCounter<ThrowingValue<>>&) const {
+    return true;
   }
 
-  friend bool AbslCheckInvariants(const InstructionCounter&) { return true; }
+  friend testing::AssertionResult AbslCheckInvariants(
+      const InstructionCounter&) {
+    return testing::AssertionSuccess();
+  }
 
   static int counter;
 };
@@ -493,18 +604,38 @@ int InstructionCounter<T>::counter = 0;
 
 TEST(ExceptionCheckTest, Exhaustiveness) {
   InstructionCounter<int> int_factory;
-  EXPECT_TRUE(TestBasicGuarantee(&int_factory, CallOperator{}));
+  EXPECT_TRUE(TestExceptionSafety(&int_factory, CallOperator{}));
   EXPECT_EQ(InstructionCounter<int>::counter, 4);
 
   InstructionCounter<ThrowingValue<>> bomb_factory;
-  EXPECT_TRUE(TestBasicGuarantee(&bomb_factory, CallOperator{}));
+  EXPECT_TRUE(TestExceptionSafety(&bomb_factory, CallOperator{}));
   EXPECT_EQ(InstructionCounter<ThrowingValue<>>::counter, 10);
 
   InstructionCounter<ThrowingValue<>>::counter = 0;
-  EXPECT_TRUE(TestStrongGuarantee(&bomb_factory, CallOperator{}));
+  EXPECT_TRUE(TestExceptionSafety(&bomb_factory, CallOperator{},
+                                  StrongGuarantee(bomb_factory)));
   EXPECT_EQ(InstructionCounter<ThrowingValue<>>::counter, 10);
 }
 
+struct LeaksIfCtorThrows : private exceptions_internal::TrackedObject {
+  LeaksIfCtorThrows() : TrackedObject(ABSL_PRETTY_FUNCTION) {
+    ++counter;
+    ThrowingValue<> v;
+    static_cast<void>(v);
+    --counter;
+  }
+  LeaksIfCtorThrows(const LeaksIfCtorThrows&) noexcept
+      : TrackedObject(ABSL_PRETTY_FUNCTION) {}
+  static int counter;
+};
+int LeaksIfCtorThrows::counter = 0;
+
+TEST(ExceptionCheckTest, TestLeakyCtor) {
+  absl::TestThrowingCtor<LeaksIfCtorThrows>();
+  EXPECT_EQ(LeaksIfCtorThrows::counter, 1);
+  LeaksIfCtorThrows::counter = 0;
+}
+
 struct Tracked : private exceptions_internal::TrackedObject {
   Tracked() : TrackedObject(ABSL_PRETTY_FUNCTION) {}
 };
diff --git a/absl/base/internal/exception_safety_testing.cc b/absl/base/internal/exception_safety_testing.cc
index 383c9c595251..32d904ed23fa 100644
--- a/absl/base/internal/exception_safety_testing.cc
+++ b/absl/base/internal/exception_safety_testing.cc
@@ -4,6 +4,7 @@
 #include "absl/meta/type_traits.h"
 
 namespace absl {
+exceptions_internal::NoThrowTag no_throw_ctor;
 namespace exceptions_internal {
 
 int countdown = -1;
@@ -14,8 +15,7 @@ void MaybeThrow(absl::string_view msg) {
 
 testing::AssertionResult FailureMessage(const TestException& e,
                                         int countdown) noexcept {
-  return testing::AssertionFailure()
-         << "Exception number " << countdown + 1 << " thrown from " << e.what();
+  return testing::AssertionFailure() << "Exception thrown from " << e.what();
 }
 }  // namespace exceptions_internal
 }  // namespace absl
diff --git a/absl/base/internal/exception_safety_testing.h b/absl/base/internal/exception_safety_testing.h
index d2742456fec3..a0a70d91d2d9 100644
--- a/absl/base/internal/exception_safety_testing.h
+++ b/absl/base/internal/exception_safety_testing.h
@@ -6,6 +6,7 @@
 #include <cstddef>
 #include <cstdint>
 #include <functional>
+#include <initializer_list>
 #include <iosfwd>
 #include <string>
 #include <unordered_map>
@@ -13,6 +14,7 @@
 #include "gtest/gtest.h"
 #include "absl/base/config.h"
 #include "absl/base/internal/pretty_function.h"
+#include "absl/memory/memory.h"
 #include "absl/meta/type_traits.h"
 #include "absl/strings/string_view.h"
 #include "absl/strings/substitute.h"
@@ -43,6 +45,8 @@ constexpr NoThrow operator&(NoThrow a, NoThrow b) {
 }
 
 namespace exceptions_internal {
+struct NoThrowTag {};
+
 constexpr bool ThrowingAllowed(NoThrow flags, NoThrow flag) {
   return !static_cast<bool>(flags & flag);
 }
@@ -92,8 +96,46 @@ class TrackedObject {
 
   friend struct ::absl::AllocInspector;
 };
+
+template <typename T, typename... Checkers>
+testing::AssertionResult TestInvariants(const T& t, const TestException& e,
+                                        int count,
+                                        const Checkers&... checkers) {
+  auto out = AbslCheckInvariants(t);
+  // Don't bother with the checkers if the class invariants are already broken.
+  bool dummy[] = {true,
+                  (out && (out = testing::AssertionResult(checkers(t))))...};
+  static_cast<void>(dummy);
+
+  return out ? out
+             : out << " Caused by exception " << count << "thrown by "
+                   << e.what();
+}
+
+template <typename T, typename EqualTo>
+class StrongGuaranteeTester {
+ public:
+  explicit StrongGuaranteeTester(std::unique_ptr<T> t_ptr, EqualTo eq) noexcept
+      : val_(std::move(t_ptr)), eq_(eq) {}
+
+  testing::AssertionResult operator()(const T& other) const {
+    return eq_(*val_, other) ? testing::AssertionSuccess()
+                             : testing::AssertionFailure() << "State changed";
+  }
+
+ private:
+  std::unique_ptr<T> val_;
+  EqualTo eq_;
+};
 }  // namespace exceptions_internal
 
+extern exceptions_internal::NoThrowTag no_throw_ctor;
+
+// These are useful for tests which just construct objects and make sure there
+// are no leaks.
+inline void SetCountdown() { exceptions_internal::countdown = 0; }
+inline void UnsetCountdown() { exceptions_internal::countdown = -1; }
+
 // A test class which is contextually convertible to bool.  The conversion can
 // be instrumented to throw at a controlled time.
 class ThrowingBool {
@@ -152,6 +194,9 @@ class ThrowingValue : private exceptions_internal::TrackedObject {
     dummy_ = i;
   }
 
+  ThrowingValue(int i, exceptions_internal::NoThrowTag) noexcept
+      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(i) {}
+
   // absl expects nothrow destructors
   ~ThrowingValue() noexcept = default;
 
@@ -173,22 +218,22 @@ class ThrowingValue : private exceptions_internal::TrackedObject {
   // Arithmetic Operators
   ThrowingValue operator+(const ThrowingValue& other) const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_ + other.dummy_, NoThrowTag{});
+    return ThrowingValue(dummy_ + other.dummy_, no_throw_ctor);
   }
 
   ThrowingValue operator+() const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_, NoThrowTag{});
+    return ThrowingValue(dummy_, no_throw_ctor);
   }
 
   ThrowingValue operator-(const ThrowingValue& other) const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_ - other.dummy_, NoThrowTag{});
+    return ThrowingValue(dummy_ - other.dummy_, no_throw_ctor);
   }
 
   ThrowingValue operator-() const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(-dummy_, NoThrowTag{});
+    return ThrowingValue(-dummy_, no_throw_ctor);
   }
 
   ThrowingValue& operator++() {
@@ -199,7 +244,7 @@ class ThrowingValue : private exceptions_internal::TrackedObject {
 
   ThrowingValue operator++(int) {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    auto out = ThrowingValue(dummy_, NoThrowTag{});
+    auto out = ThrowingValue(dummy_, no_throw_ctor);
     ++dummy_;
     return out;
   }
@@ -212,34 +257,34 @@ class ThrowingValue : private exceptions_internal::TrackedObject {
 
   ThrowingValue operator--(int) {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    auto out = ThrowingValue(dummy_, NoThrowTag{});
+    auto out = ThrowingValue(dummy_, no_throw_ctor);
     --dummy_;
     return out;
   }
 
   ThrowingValue operator*(const ThrowingValue& other) const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_ * other.dummy_, NoThrowTag{});
+    return ThrowingValue(dummy_ * other.dummy_, no_throw_ctor);
   }
 
   ThrowingValue operator/(const ThrowingValue& other) const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_ / other.dummy_, NoThrowTag{});
+    return ThrowingValue(dummy_ / other.dummy_, no_throw_ctor);
   }
 
   ThrowingValue operator%(const ThrowingValue& other) const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_ % other.dummy_, NoThrowTag{});
+    return ThrowingValue(dummy_ % other.dummy_, no_throw_ctor);
   }
 
   ThrowingValue operator<<(int shift) const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_ << shift, NoThrowTag{});
+    return ThrowingValue(dummy_ << shift, no_throw_ctor);
   }
 
   ThrowingValue operator>>(int shift) const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_ >> shift, NoThrowTag{});
+    return ThrowingValue(dummy_ >> shift, no_throw_ctor);
   }
 
   // Comparison Operators
@@ -293,22 +338,22 @@ class ThrowingValue : private exceptions_internal::TrackedObject {
   // Bitwise Logical Operators
   ThrowingValue operator~() const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(~dummy_, NoThrowTag{});
+    return ThrowingValue(~dummy_, no_throw_ctor);
   }
 
   ThrowingValue operator&(const ThrowingValue& other) const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_ & other.dummy_, NoThrowTag{});
+    return ThrowingValue(dummy_ & other.dummy_, no_throw_ctor);
   }
 
   ThrowingValue operator|(const ThrowingValue& other) const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_ | other.dummy_, NoThrowTag{});
+    return ThrowingValue(dummy_ | other.dummy_, no_throw_ctor);
   }
 
   ThrowingValue operator^(const ThrowingValue& other) const {
     exceptions_internal::MaybeThrow(ABSL_PRETTY_FUNCTION);
-    return ThrowingValue(dummy_ ^ other.dummy_, NoThrowTag{});
+    return ThrowingValue(dummy_ ^ other.dummy_, no_throw_ctor);
   }
 
   // Compound Assignment operators
@@ -434,10 +479,6 @@ class ThrowingValue : private exceptions_internal::TrackedObject {
   const int& Get() const noexcept { return dummy_; }
 
  private:
-  struct NoThrowTag {};
-  ThrowingValue(int i, NoThrowTag) noexcept
-      : TrackedObject(ABSL_PRETTY_FUNCTION), dummy_(i) {}
-
   int dummy_;
 };
 // While not having to do with exceptions, explicitly delete comma operator, to
@@ -596,7 +637,9 @@ int ThrowingAllocator<T, Throws>::next_id_ = 0;
 
 // Inspects the constructions and destructions of anything inheriting from
 // TrackedObject.  Place this as a member variable in a test fixture to ensure
-// that every ThrowingValue was constructed and destroyed correctly.
+// that every ThrowingValue was constructed and destroyed correctly.  This also
+// allows us to safely "leak" TrackedObjects, as AllocInspector will destroy
+// everything left over in its destructor.
 struct AllocInspector {
   AllocInspector() = default;
   ~AllocInspector() {
@@ -609,69 +652,79 @@ struct AllocInspector {
   }
 };
 
-// Tests that performing operation Op on a T follows the basic exception safety
-// guarantee.
-//
-// Parameters:
-//   * T: the type under test.
-//   * FunctionFromTPtrToVoid: A functor exercising the function under test.  It
-//     should take a T* and return void.
-//
-//  There must also be a function named `AbslCheckInvariants` in an associated
-//  namespace of T which takes a const T& and returns true if the T's class
-//  invariants hold, and false if they don't.
-template <typename T, typename FunctionFromTPtrToVoid>
-testing::AssertionResult TestBasicGuarantee(T* t, FunctionFromTPtrToVoid&& op) {
+// Tests for resource leaks by attempting to construct a T using args repeatedly
+// until successful, using the countdown method.  Side effects can then be
+// tested for resource leaks.  If an AllocInspector is present in the test
+// fixture, then this will also test that memory resources are not leaked as
+// long as T allocates TrackedObjects.
+template <typename T, typename... Args>
+T TestThrowingCtor(Args&&... args) {
+  struct Cleanup {
+    ~Cleanup() { UnsetCountdown(); }
+  };
+  Cleanup c;
   for (int countdown = 0;; ++countdown) {
     exceptions_internal::countdown = countdown;
     try {
-      op(t);
-      break;
-    } catch (const exceptions_internal::TestException& e) {
-      if (!AbslCheckInvariants(*t)) {
-        return exceptions_internal::FailureMessage(e, countdown)
-               << " broke invariants.";
-      }
+      return T(std::forward<Args>(args)...);
+    } catch (const exceptions_internal::TestException&) {
     }
   }
-  exceptions_internal::countdown = -1;
-  return testing::AssertionSuccess();
 }
 
-// Tests that performing operation Op on a T follows the strong exception safety
-// guarantee.
+// Tests that performing operation Op on a T follows exception safety
+// guarantees.  By default only tests the basic guarantee.
 //
 // Parameters:
-//   * T: the type under test. T must be copy-constructable and
-//   equality-comparible.
+//   * T: the type under test.
 //   * FunctionFromTPtrToVoid: A functor exercising the function under test.  It
-//     should take a T* and return void.
-//
-//  There must also be a function named `AbslCheckInvariants` in an associated
-//  namespace of T which takes a const T& and returns true if the T's class
-//  invariants hold, and false if they don't.
-template <typename T, typename FunctionFromTPtrToVoid>
-testing::AssertionResult TestStrongGuarantee(T* t,
-                                             FunctionFromTPtrToVoid&& op) {
-  exceptions_internal::countdown = -1;
-  for (auto countdown = 0;; ++countdown) {
-    T dup = *t;
+//   should take a T* and return void.
+//   * Checkers: Any number of functions taking a const T& and returning
+//   anything contextually convertible to bool.  If a testing::AssertionResult
+//   is used then the error message is kept.  These test invariants related to
+//   the operation. To test the strong guarantee, pass
+//   absl::StrongGuarantee(...) as one of these arguments if T has operator==.
+//   Some types for which the strong guarantee makes sense don't have operator==
+//   (eg std::any).  A function capturing *t or a T equal to it, taking a const
+//   T&, and returning contextually-convertible-to-bool may be passed instead.
+template <typename T, typename FunctionFromTPtrToVoid, typename... Checkers>
+testing::AssertionResult TestExceptionSafety(T* t, FunctionFromTPtrToVoid&& op,
+                                             const Checkers&... checkers) {
+  auto out = testing::AssertionSuccess();
+  for (int countdown = 0;; ++countdown) {
     exceptions_internal::countdown = countdown;
     try {
       op(t);
       break;
     } catch (const exceptions_internal::TestException& e) {
-      if (!AbslCheckInvariants(*t)) {
-        return exceptions_internal::FailureMessage(e, countdown)
-               << " broke invariants.";
-      }
-      if (dup != *t)
-        return exceptions_internal::FailureMessage(e, countdown)
-               << " changed state.";
+      out = exceptions_internal::TestInvariants(*t, e, countdown, checkers...);
+      if (!out) return out;
     }
   }
-  exceptions_internal::countdown = -1;
-  return testing::AssertionSuccess();
+  UnsetCountdown();
+  return out;
+}
+
+// Returns a functor to test for the strong exception-safety guarantee.  If T is
+// copyable, use the const T& overload, otherwise pass a unique_ptr<T>.
+// Equality comparisons are made against the T provided and default to using
+// operator==.  See the documentation for TestExceptionSafety if T doesn't have
+// operator== but the strong guarantee still makes sense for it.
+//
+// Parameters:
+//   * T: The type under test.
+template <typename T, typename EqualTo = std::equal_to<T>>
+exceptions_internal::StrongGuaranteeTester<T, EqualTo> StrongGuarantee(
+    const T& t, EqualTo eq = EqualTo()) {
+  return exceptions_internal::StrongGuaranteeTester<T, EqualTo>(
+      absl::make_unique<T>(t), eq);
+}
+
+template <typename T, typename EqualTo = std::equal_to<T>>
+exceptions_internal::StrongGuaranteeTester<T, EqualTo> PointeeStrongGuarantee(
+    std::unique_ptr<T> t_ptr, EqualTo eq = EqualTo()) {
+  return exceptions_internal::StrongGuaranteeTester<T, EqualTo>(
+      std::move(t_ptr), eq);
 }
 
 }  // namespace absl