Google单元测试sample分析（四）

GoogleTest单元测试可用实现在每个测试用例结束后监控其内存使用情况，

可以通过GoogleTest提供的事件侦听器EmptyTestEventListener 来实现，下面通过官方提供的sample例子，路径在samples文件夹下的sample10_unittest.cpp

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// This sample shows how to use Google Test listener API to implement
// a primitive leak checker.

#include 
#include 

#include "gtest/gtest.h"
using ::testing::EmptyTestEventListener;
using ::testing::InitGoogleTest;
using ::testing::Test;
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.
  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_;
};

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);
}
}  // 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();
}

通过Water类来重写new和delete方法来实现记录内存分配/释放的情况，另外通过LeakChecker 继承自EmptyTestEventListener 并实现OnTestStart（测试用例开始前运行）和OnTestEnd方法（测试用例结束后运行）

关于LeakChecker的使用是先获取系统提供的listeners ，然后把自定义事件加入到系统中去即可。
TestEventListeners& listeners = UnitTest::GetInstance()->listeners();
listeners.Append(new LeakChecker);