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+// Copyright (c) 2007, Google Inc.
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: Zhanyong Wan
+//
+// Defines the ScopedMockLog class (using Google C++ Mocking
+// Framework), which is convenient for testing code that uses LOG().
+
+#ifndef GLOG_SRC_MOCK_LOG_H_
+#define GLOG_SRC_MOCK_LOG_H_
+
+// For GOOGLE_NAMESPACE. This must go first so we get _XOPEN_SOURCE.
+#include "utilities.h"
+
+#include <string>
+
+#include <gmock/gmock.h>
+
+#include "glog/logging.h"
+
+_START_GOOGLE_NAMESPACE_
+namespace glog_testing {
+
+// A ScopedMockLog object intercepts LOG() messages issued during its
+// lifespan.  Using this together with Google C++ Mocking Framework,
+// it's very easy to test how a piece of code calls LOG().  The
+// typical usage:
+//
+//   TEST(FooTest, LogsCorrectly) {
+//     ScopedMockLog log;
+//
+//     // We expect the WARNING "Something bad!" exactly twice.
+//     EXPECT_CALL(log, Log(WARNING, _, "Something bad!"))
+//         .Times(2);
+//
+//     // We allow foo.cc to call LOG(INFO) any number of times.
+//     EXPECT_CALL(log, Log(INFO, HasSubstr("/foo.cc"), _))
+//         .Times(AnyNumber());
+//
+//     Foo();  // Exercises the code under test.
+//   }
+class ScopedMockLog : public GOOGLE_NAMESPACE::LogSink {
+ public:
+  // When a ScopedMockLog object is constructed, it starts to
+  // intercept logs.
+  ScopedMockLog() { AddLogSink(this); }
+
+  // When the object is destructed, it stops intercepting logs.
+  virtual ~ScopedMockLog() { RemoveLogSink(this); }
+
+  // Implements the mock method:
+  //
+  //   void Log(LogSeverity severity, const string& file_path,
+  //            const string& message);
+  //
+  // The second argument to Send() is the full path of the source file
+  // in which the LOG() was issued.
+  //
+  // Note, that in a multi-threaded environment, all LOG() messages from a
+  // single thread will be handled in sequence, but that cannot be guaranteed
+  // for messages from different threads. In fact, if the same or multiple
+  // expectations are matched on two threads concurrently, their actions will
+  // be executed concurrently as well and may interleave.
+  MOCK_METHOD3(Log, void(GOOGLE_NAMESPACE::LogSeverity severity,
+                         const std::string& file_path,
+                         const std::string& message));
+
+ private:
+  // Implements the send() virtual function in class LogSink.
+  // Whenever a LOG() statement is executed, this function will be
+  // invoked with information presented in the LOG().
+  //
+  // The method argument list is long and carries much information a
+  // test usually doesn't care about, so we trim the list before
+  // forwarding the call to Log(), which is much easier to use in
+  // tests.
+  //
+  // We still cannot call Log() directly, as it may invoke other LOG()
+  // messages, either due to Invoke, or due to an error logged in
+  // Google C++ Mocking Framework code, which would trigger a deadlock
+  // since a lock is held during send().
+  //
+  // Hence, we save the message for WaitTillSent() which will be called after
+  // the lock on send() is released, and we'll call Log() inside
+  // WaitTillSent(). Since while a single send() call may be running at a
+  // time, multiple WaitTillSent() calls (along with the one send() call) may
+  // be running simultaneously, we ensure thread-safety of the exchange between
+  // send() and WaitTillSent(), and that for each message, LOG(), send(),
+  // WaitTillSent() and Log() are executed in the same thread.
+  virtual void send(GOOGLE_NAMESPACE::LogSeverity severity,
+                    const char* full_filename,
+                    const char* /*base_filename*/, int /*line*/,
+                    const tm* /*tm_time*/,
+                    const char* message, size_t message_len) {
+    // We are only interested in the log severity, full file name, and
+    // log message.
+    message_info_.severity = severity;
+    message_info_.file_path = full_filename;
+    message_info_.message = std::string(message, message_len);
+  }
+
+  // Implements the WaitTillSent() virtual function in class LogSink.
+  // It will be executed after send() and after the global logging lock is
+  // released, so calls within it (or rather within the Log() method called
+  // within) may also issue LOG() statements.
+  //
+  // LOG(), send(), WaitTillSent() and Log() will occur in the same thread for
+  // a given log message.
+  virtual void WaitTillSent() {
+    // First, and very importantly, we save a copy of the message being
+    // processed before calling Log(), since Log() may indirectly call send()
+    // and WaitTillSent() in the same thread again.
+    MessageInfo message_info = message_info_;
+    Log(message_info.severity, message_info.file_path, message_info.message);
+  }
+
+  // All relevant information about a logged message that needs to be passed
+  // from send() to WaitTillSent().
+  struct MessageInfo {
+    GOOGLE_NAMESPACE::LogSeverity severity;
+    std::string file_path;
+    std::string message;
+  };
+  MessageInfo message_info_;
+};
+
+}  // namespace glog_testing
+_END_GOOGLE_NAMESPACE_
+
+#endif  // GLOG_SRC_MOCK_LOG_H_