Google C++单元测试框架GoogleTest---Extending Google Test by Handling Test Events

Google TestExtending Google Test by Handling Test Events

Google测试提供了一个事件侦听器API，让您接收有关测试程序进度和测试失败的通知。 可以监听的事件包括测试程序的开始和结束，测试用例或测试方法等。 您可以使用此API来扩充或替换标准控制台输出，替换XML输出，或提供完全不同的输出形式，例如GUI或数据库。 例如，您还可以使用测试事件作为检查点来实现资源泄漏检查器。

一、定义事件侦听器

要定义一个事件监听器，你需要继承testing :: TestEventListener或testing :: EmptyTestEventListener。前者是一个（抽象）接口，其中每个纯虚方法
可以重写以处理测试事件（例如，当测试开始时，将调用OnTestStart()方法。）。后者提供了接​​口中所有方法的空实现，使得子类只需要覆盖它关心的方法。

当一个事件触发时，它的上下文作为参数传递给处理函数。使用以下参数类型：

• UnitTest反映整个测试程序的状态，
• TestCase包含关于一个测试用例的信息，它可以包含一个或多个测试，
• TestInfo包含测试的状态，和
• TestPartResult表示测试断言的结果。

事件处理函数可以检查它接收的参数，以找到关于事件和测试程序状态的有趣信息。这里有一个例子：

class MinimalistPrinter : public ::testing::EmptyTestEventListener {
    // Called before a test starts.
    virtual void OnTestStart(const ::testing::TestInfo& test_info) {
      printf("*** Test %s.%s starting.\n",
             test_info.test_case_name(), test_info.name());
    }

    // Called after a failed assertion or a SUCCEED() invocation.
    virtual void OnTestPartResult(
        const ::testing::TestPartResult& test_part_result) {
      printf("%s in %s:%d\n%s\n",
             test_part_result.failed() ? "*** Failure" : "Success",
             test_part_result.file_name(),
             test_part_result.line_number(),
             test_part_result.summary());
    }

    // Called after a test ends.
    virtual void OnTestEnd(const ::testing::TestInfo& test_info) {
      printf("*** Test %s.%s ending.\n",
             test_info.test_case_name(), test_info.name());
    }
  };

二、使用事件监听器

要使用您定义的事件侦听器，请将其实例添加到Google Test事件侦听器列表中（由TestEventListeners类表示）

• note the "s" at the end of the name) in your main() function, before calling RUN_ALL_TESTS():

int main(int argc, char** argv) {
  ::testing::InitGoogleTest(&argc, argv);
  // Gets hold of the event listener list.
  ::testing::TestEventListeners& listeners =
      ::testing::UnitTest::GetInstance()->listeners();
  // Adds a listener to the end.  Google Test takes the ownership.
  listeners.Append(new MinimalistPrinter);
  return RUN_ALL_TESTS();
}

　　只有一个问题：默认测试结果打印机仍然有效，因此其输出将与您的简约打印机的输出混合。 要禁止默认打印机，只需从事件侦听器列表中释放它并删除它。 您可以添加一行：

...
  delete listeners.Release(listeners.default_result_printer());
  listeners.Append(new MinimalistPrinter);
  return RUN_ALL_TESTS();

现在，坐下来享受与你的测试完全不同的输出。 有关更多详细信息，您可以阅读此示例 sample(sample9_unittest)。

您可以向列表附加多个侦听器。 当On * Start（）或OnTestPartResult（）事件触发时，监听器将按它们在列表中显示的顺序接收它（因为新的监听器添加到列表的末尾，默认文本打印机和默认XML生成器 将第一时间接收事件）。 An On * End（）事件将由侦听器以相反的顺序接收。 这允许稍后添加的侦听器的输出由之前添加的侦听器的输出构成。

三、Generating Failures in Listeners

在处理事件时，可以使用故障提升宏（EXPECT _ *()，ASSERT _ *()，FAIL()等）。 有一些限制：

• 你不能在OnTestPartResult（）中产生任何失败（否则会导致OnTestPartResult（）被递归调用）。
• 处理OnTestPartResult（）的侦听器不允许生成任何失败。

当您向侦听器列表添加侦听器时，应该在可能生成失败的侦听器之前放置处理OnTestPartResult（）的侦听器。 这确保由后者产生的故障归因于前者的正确测试。

我们在这里有一个失败监听器的示例here（sample10_unittest）。

四、TestEventListener接口

// The interface for tracing execution of tests. The methods are organized in
// the order the corresponding events are fired.
class TestEventListener {
 public:
  virtual ~TestEventListener() {}

  // Fired before any test activity starts.
  virtual void OnTestProgramStart(const UnitTest& unit_test) = 0;

  // Fired before each iteration of tests starts.  There may be more than
  // one iteration if GTEST_FLAG(repeat) is set. iteration is the iteration
  // index, starting from 0.
  virtual void OnTestIterationStart(const UnitTest& unit_test,
                                    int iteration) = 0;

  // Fired before environment set-up for each iteration of tests starts.
  virtual void OnEnvironmentsSetUpStart(const UnitTest& unit_test) = 0;

  // Fired after environment set-up for each iteration of tests ends.
  virtual void OnEnvironmentsSetUpEnd(const UnitTest& unit_test) = 0;

  // Fired before the test case starts.
  virtual void OnTestCaseStart(const TestCase& test_case) = 0;

  // Fired before the test starts.
  virtual void OnTestStart(const TestInfo& test_info) = 0;

  // Fired after a failed assertion or a SUCCEED() invocation.
  virtual void OnTestPartResult(const TestPartResult& test_part_result) = 0;

  // Fired after the test ends.
  virtual void OnTestEnd(const TestInfo& test_info) = 0;

  // Fired after the test case ends.
  virtual void OnTestCaseEnd(const TestCase& test_case) = 0;

  // Fired before environment tear-down for each iteration of tests starts.
  virtual void OnEnvironmentsTearDownStart(const UnitTest& unit_test) = 0;

  // Fired after environment tear-down for each iteration of tests ends.
  virtual void OnEnvironmentsTearDownEnd(const UnitTest& unit_test) = 0;

  // Fired after each iteration of tests finishes.
  virtual void OnTestIterationEnd(const UnitTest& unit_test,
                                  int iteration) = 0;

  // Fired after all test activities have ended.
  virtual void OnTestProgramEnd(const UnitTest& unit_test) = 0;
};

// The convenience class for users who need to override just one or two
// methods and are not concerned that a possible change to a signature of
// the methods they override will not be caught during the build.  For
// comments about each method please see the definition of TestEventListener
// above.一个空实现
class EmptyTestEventListener : public TestEventListener {
 public:
  virtual void OnTestProgramStart(const UnitTest& /*unit_test*/) {}
  virtual void OnTestIterationStart(const UnitTest& /*unit_test*/,
                                    int /*iteration*/) {}
  virtual void OnEnvironmentsSetUpStart(const UnitTest& /*unit_test*/) {}
  virtual void OnEnvironmentsSetUpEnd(const UnitTest& /*unit_test*/) {}
  virtual void OnTestCaseStart(const TestCase& /*test_case*/) {}
  virtual void OnTestStart(const TestInfo& /*test_info*/) {}
  virtual void OnTestPartResult(const TestPartResult& /*test_part_result*/) {}
  virtual void OnTestEnd(const TestInfo& /*test_info*/) {}
  virtual void OnTestCaseEnd(const TestCase& /*test_case*/) {}
  virtual void OnEnvironmentsTearDownStart(const UnitTest& /*unit_test*/) {}
  virtual void OnEnvironmentsTearDownEnd(const UnitTest& /*unit_test*/) {}
  virtual void OnTestIterationEnd(const UnitTest& /*unit_test*/,
                                  int /*iteration*/) {}
  virtual void OnTestProgramEnd(const UnitTest& /*unit_test*/) {}
};

五、官方例子

就是samples文件夹下的sample10_unittest.cpp

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

#include "stdafx.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();
}