Google单元测试框架gtest之官方sample笔记4--事件监控之内存泄漏测试

sample 10 使用event listener监控Water类的创建和销毁。在Water类中，有一个静态变量allocated，创建一次值加一，销毁一次值减一。为了实现这个功能，重载了new和delete关键字，然后在new和delete函数中，做allocated的增减和记录allocated变量的值。

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;

gtest的event listener能在TEST执行前和执行后调用，然后就可以判断TEST执行完后是否发生泄漏。event listner是非入侵式检测，不需要在TEST里写测试代码，而是在TEST之外执行特定的监控代码。

注册event监听的方法如下，在每个测试前执行OnTestStart，在测试后执行OnTestEnd。计算int difference = Water::allocated() - initially_allocated_;就可以得知是否发生内存泄漏，忘记了删除new的对象。

class LeakChecker : public EmptyTestEventListener {
 private:
  // Called before a test starts.
  void OnTestStart(const TestInfo&  test_info ) override {
    initially_allocated_ = Water::allocated();
  }

  // Called after a test ends.
  void OnTestEnd(const TestInfo& /* test_info */) override {
    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_;
};

// 如果检查泄漏，则注册event listener监控
if (check_for_leaks) {
    TestEventListeners& listeners = UnitTest::GetInstance()->listeners();
    listeners.Append(new LeakChecker);
}

测试代码如下，由于使用的是非入侵式检测，所以TEST函数和普通的测试一样。下面的DoesNotLeak测试无内存泄漏发生，而LeaksWater测试，会发生内存泄漏。

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 != nullptr);
}

不启用内存泄漏测试时的输出结果：