本文开始从googletest提供的sample案例分析如何使用单元测试，

代码路径在googletest/googletest/samples/sample1.unittest.cc
本文件主要介绍EXPECT*相关宏使用

EXPECT_EQ 判断是否相等
EXPECT_TRUE 是否为True
EXPECT_FALSE 是否为False

TEST(FactorialTest, Negative) {
  // This test is named "Negative", and belongs to the "FactorialTest"
  // test case.
  EXPECT_EQ(1, Factorial(-5));
  EXPECT_EQ(1, Factorial(-1));
  EXPECT_GT(Factorial(-10), 0);

  // <TechnicalDetails>
  //
  // EXPECT_EQ(expected, actual) is the same as
  //
  //   EXPECT_TRUE((expected) == (actual))
  //
  // except that it will print both the expected value and the actual
  // value when the assertion fails.  This is very helpful for
  // debugging.  Therefore in this case EXPECT_EQ is preferred.
  //
  // On the other hand, EXPECT_TRUE accepts any Boolean expression,
  // and is thus more general.
  //
  // </TechnicalDetails>
}

下面介绍sample2_unittest.cc文件

这里测试MyString类，
EXPECT_STREQ(nullptr, s.c_string()); //这里的STREQ是判断字符串内容，s为空类比较要使用nullptr

TEST(MyString, DefaultConstructor) {
  const MyString s;

  // Asserts that s.c_string() returns NULL.
  //
  // <TechnicalDetails>
  //
  // If we write NULL instead of
  //
  //   static_cast<const char *>(NULL)
  //
  // in this assertion, it will generate a warning on gcc 3.4.  The
  // reason is that EXPECT_EQ needs to know the types of its
  // arguments in order to print them when it fails.  Since NULL is
  // #defined as 0, the compiler will use the formatter function for
  // int to print it.  However, gcc thinks that NULL should be used as
  // a pointer, not an int, and therefore complains.
  //
  // The root of the problem is C++'s lack of distinction between the
  // integer number 0 and the null pointer constant.  Unfortunately,
  // we have to live with this fact.
  //
  // </TechnicalDetails>
  EXPECT_STREQ(nullptr, s.c_string());

  EXPECT_EQ(0u, s.Length());
}