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+// Copyright 2009 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: vladl@google.com (Vlad Losev)
+
+// This sample shows how to use Google Test listener API to implement
+// a primitive leak checker.
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "gtest/gtest.h"
+
+using ::testing::EmptyTestEventListener;
+using ::testing::InitGoogleTest;
+using ::testing::Test;
+using ::testing::TestCase;
+using ::testing::TestEventListeners;
+using ::testing::TestInfo;
+using ::testing::TestPartResult;
+using ::testing::UnitTest;
+
+namespace {
+
+// We will track memory used by this class.
+class Water {
+ public:
+  // Normal Water declarations go here.
+
+  // operator new and operator delete help us control water allocation.
+  void* operator new(size_t allocation_size) {
+    allocated_++;
+    return malloc(allocation_size);
+  }
+
+  void operator delete(void* block, size_t /* allocation_size */) {
+    allocated_--;
+    free(block);
+  }
+
+  static int allocated() { return allocated_; }
+
+ private:
+  static int allocated_;
+};
+
+int Water::allocated_ = 0;
+
+// This event listener monitors how many Water objects are created and
+// destroyed by each test, and reports a failure if a test leaks some Water
+// objects. It does this by comparing the number of live Water objects at
+// the beginning of a test and at the end of a test.
+class LeakChecker : public EmptyTestEventListener {
+ private:
+  // Called before a test starts.
+  virtual void OnTestStart(const TestInfo& /* test_info */) {
+    initially_allocated_ = Water::allocated();
+  }
+
+  // Called after a test ends.
+  virtual void OnTestEnd(const TestInfo& /* test_info */) {
+    int difference = Water::allocated() - initially_allocated_;
+
+    // You can generate a failure in any event handler except
+    // OnTestPartResult. Just use an appropriate Google Test assertion to do
+    // it.
+    EXPECT_LE(difference, 0) << "Leaked " << difference << " unit(s) of Water!";
+  }
+
+  int initially_allocated_;
+};
+
+TEST(ListenersTest, DoesNotLeak) {
+  Water* water = new Water;
+  delete water;
+}
+
+// This should fail when the --check_for_leaks command line flag is
+// specified.
+TEST(ListenersTest, LeaksWater) {
+  Water* water = new Water;
+  EXPECT_TRUE(water != NULL);
+}
+
+}  // namespace
+
+int main(int argc, char **argv) {
+  InitGoogleTest(&argc, argv);
+
+  bool check_for_leaks = false;
+  if (argc > 1 && strcmp(argv[1], "--check_for_leaks") == 0 )
+    check_for_leaks = true;
+  else
+    printf("%s\n", "Run this program with --check_for_leaks to enable "
+           "custom leak checking in the tests.");
+
+  // If we are given the --check_for_leaks command line flag, installs the
+  // leak checker.
+  if (check_for_leaks) {
+    TestEventListeners& listeners = UnitTest::GetInstance()->listeners();
+
+    // Adds the leak checker to the end of the test event listener list,
+    // after the default text output printer and the default XML report
+    // generator.
+    //
+    // The order is important - it ensures that failures generated in the
+    // leak checker's OnTestEnd() method are processed by the text and XML
+    // printers *before* their OnTestEnd() methods are called, such that
+    // they are attributed to the right test. Remember that a listener
+    // receives an OnXyzStart event *after* listeners preceding it in the
+    // list received that event, and receives an OnXyzEnd event *before*
+    // listeners preceding it.
+    //
+    // We don't need to worry about deleting the new listener later, as
+    // Google Test will do it.
+    listeners.Append(new LeakChecker);
+  }
+  return RUN_ALL_TESTS();
+}