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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//
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//
// 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,
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// 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.// 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::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);
}
}  // namespaceint 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;elseprintf("%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);