Google單元測試框架gtest之官方sample筆記4–事件監控之內存泄漏測試

sample 10 使用event listener監控Water類的創建和銷毀。在Water類中，有一個靜態變量allocated，創建一次值加一，銷毀一次值減一。為了實現這個功能，重載了new和delete關鍵字，然後在new和delete函數中，做allocated的增減和記錄allocated變量的值。

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執行前和執行後調用，然後就可以判斷TEST執行完後是否發生泄漏。event listner是非入侵式檢測，不需要在TEST里寫測試代碼，而是在TEST之外執行特定的監控代碼。

註冊event監聽的方法如下，在每個測試前執行OnTestStart，在測試後執行OnTestEnd。計算int difference = Water::allocated() – initially_allocated_;就可以得知是否發生內存泄漏，忘記了刪除new的對象。

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_;
};
​
// 如果檢查泄漏，則註冊event listener監控
if (check_for_leaks) {
    TestEventListeners& listeners = UnitTest::GetInstance()->listeners();
    listeners.Append(new LeakChecker);
}

測試代碼如下，由於使用的是非入侵式檢測，所以TEST函數和普通的測試一樣。下面的DoesNotLeak測試無內存泄漏發生，而LeaksWater測試，會發生內存泄漏。

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);
}

不啟用內存泄漏測試時的輸出結果：

使用內存泄漏測試時的輸出結果：

 

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Google單元測試框架gtest之官方sample筆記4–事件監控之內存泄漏測試

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