Chromium roll (https://codereview.chromium.org/976353002)

base/test/mock_log.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_TEST_MOCK_LOG_H_
+#define BASE_TEST_MOCK_LOG_H_
+
+#include <string>
+
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/synchronization/lock.h"
+#include "testing/gmock/include/gmock/gmock.h"
+
+namespace base {
+namespace test {
+
+// A MockLog object intercepts LOG() messages issued during its lifespan.  Using
+// this together with gMock, it's very easy to test how a piece of code calls
+// LOG().  The typical usage:
+//
+//   TEST(FooTest, LogsCorrectly) {
+//     MockLog 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());
+//
+//     log.StartCapturingLogs();  // Call this after done setting expectations.
+//     Foo();  // Exercises the code under test.
+//   }
+//
+// CAVEAT: base/logging does not allow a thread to call LOG() again when it's
+// already inside a LOG() call.  Doing so will cause a deadlock.  Therefore,
+// it's the user's responsibility to not call LOG() in an action triggered by
+// MockLog::Log().  You may call RAW_LOG() instead.
+class MockLog {
+ public:
+  // Creates a MockLog object that is not capturing logs.  If it were to start
+  // to capture logs, it could be a problem if some other threads already exist
+  // and are logging, as the user hasn't had a chance to set up expectation on
+  // this object yet (calling a mock method before setting the expectation is
+  // UNDEFINED behavior).
+  MockLog();
+
+  // When the object is destructed, it stops intercepting logs.
+  ~MockLog();
+
+  // Starts log capturing if the object isn't already doing so.
+  // Otherwise crashes.
+  void StartCapturingLogs();
+
+  // Stops log capturing if the object is capturing logs.  Otherwise crashes.
+  void StopCapturingLogs();
+
+  // Log method is invoked for every log message before it's sent to other log
+  // destinations (if any).  The method should return true to signal that it
+  // handled the message and the message should not be sent to other log
+  // destinations.
+  MOCK_METHOD5(Log,
+               bool(int severity,
+                    const char* file,
+                    int line,
+                    size_t message_start,
+                    const std::string& str));
+
+ private:
+  // The currently active mock log.
+  static MockLog* g_instance_;
+
+  // Lock protecting access to g_instance_.
+  static Lock g_lock;
+
+  // Static function which is set as the logging message handler.
+  // Called once for each message.
+  static bool LogMessageHandler(int severity,
+                                const char* file,
+                                int line,
+                                size_t message_start,
+                                const std::string& str);
+
+  // True if this object is currently capturing logs.
+  bool is_capturing_logs_;
+
+  // The previous handler to restore when the MockLog is destroyed.
+  logging::LogMessageHandlerFunction previous_handler_;
+
+  DISALLOW_COPY_AND_ASSIGN(MockLog);
+};
+
+}  // namespace test
+}  // namespace base
+
+#endif  // BASE_TEST_MOCK_LOG_H_