断言
########################################

前言
****************************************

这篇文章主要总结gtest中的所有断言相关的宏。 gtest中，断言的宏可以理解为分为两类，一类是ASSERT系列，一类是EXPECT系列。一个直观的解释就是：

1. ASSERT_* 系列的断言，当检查点失败时，退出当前函数（注意：并非退出当前案例）。
2. EXPECT_* 系列的断言，当检查点失败时，继续往下执行。

示例
****************************************

.. code-block:: cpp

   // int型比较，预期值：3，实际值：Add(1, 2)
   EXPECT_EQ(3, Add(1, 2))
   //

假如你的Add(1, 2) 结果为4的话，会在结果中输出：

.. code-block:: none

   g:\myproject\c++\gtestdemo\gtestdemo\gtestdemo.cpp(16): error: Value of: Add(1, 2)
   Actual: 4
   Expected:3

如果是将结果输出到xml里的话，将输出：（关于将结果输出为xml，见：http://www.cnblogs.com/coderzh/archive/2009/04/10/1432789.html）

.. code-block:: xml

   <testcase name="Demo" status="run" time="0" classname="AddTest">      <failure message="Value of: Add(1, 2)
   Actual: 4
   Expected: 3" type=""><![CDATA[g:\myproject\c++\gtestdemo\gtestdemo\gtestdemo.cpp:16Value of: Add(1, 2)  Actual: 4Expected: 3]]></failure></testcase>

如果你对自动输出的出错信息不满意的话，你还可以通过操作符<<将一些自定义的信息输出，通常，这对于调试或是对一些检查点的补充说明来说，非常有用！

下面举个例子：

如果不使用<<操作符自定义输出的话：

.. code-block:: cpp

   for (int i = 0; i < x.size(); ++i)
   {
      EXPECT_EQ(x[i], y[i]);
   }

看到的结果将是这样的，你根本不知道出错时 i 等于几：

.. code-block:: none

   g:\myproject\c++\gtestdemo\gtestdemo\gtestdemo.cpp(25): error: Value of: y[i]
   Actual: 4
   Expected: x[i]
   Which is: 3

如果使用<<操作符将一些重要信息输出的话：

.. code-block:: cpp

   for (int i = 0; i < x.size(); ++i)
   {
      EXPECT_EQ(x[i], y[i]) << "Vectors x and y differ at index " << i;
   }

从输出结果中就可以定位到在 i = 2 时出现了错误。这样的输出结果看起来更加有用，容易理解：

.. code-block:: none

   g:\myproject\c++\gtestdemo\gtestdemo\gtestdemo.cpp(25): error: Value of: y[i]
   Actual: 4
   Expected: x[i]
   Which is: 3
   Vectors x and y differ at index 2

布尔值检查
****************************************

.. csv-table::
   :header: Fatal assertion, Nonfatal assertion, Verifies

   ASSERT_TRUE(condition); , EXPECT_TRUE(condition);, condition is true
   ASSERT_FALSE(condition);,EXPECT_FALSE(condition);, condition is false

数值型数据检查
****************************************

============================  ============================  ==================
Fatal assertion                 Nonfatal assertion            Verifies
============================  ============================  ==================
ASSERT_EQ(expected, actual);  EXPECT_EQ(expected, actual);  expected == actual
ASSERT_NE(val1, val2);        EXPECT_NE(val1, val2);        val1 != val2
ASSERT_LT(val1, val2);        EXPECT_LT(val1, val2);        val1 < val2
ASSERT_LE(val1, val2);        EXPECT_LE(val1, val2);        val1 <= val2
ASSERT_GT(val1, val2);        EXPECT_GT(val1, val2);        val1 > val2
ASSERT_GE(val1, val2);        EXPECT_GE(val1, val2);        val1 >= val2
============================  ============================  ==================

字符串检查
****************************************

===========================================  ============================================  =============================================================
Fatal assertion                                Nonfatal assertion                                    Verifies
===========================================  ============================================  =============================================================
ASSERT_STREQ(expected_str, actual_str);      ,EXPECT_STREQ(expected_str, actual_str);      ,the two C strings have the same content
ASSERT_STRNE(str1, str2);                    ,EXPECT_STRNE(str1, str2);                    ,the two C strings have different content
ASSERT_STRCASEEQ(expected_str, actual_str);  ,EXPECT_STRCASEEQ(expected_str, actual_str);  ,the two C strings have the same content, ignoring case
ASSERT_STRCASENE(str1, str2);                ,EXPECT_STRCASENE(str1, str2);                ,the two C strings have different content, ignoring case
===========================================  ============================================  =============================================================

*STREQ* 和 *STRNE* 同时支持 char\* 和 wchar_t\* 类型的，*STRCASEEQ* 和 *STRCASENE* 却只接收char*，估计是不常用吧。下面是几个例子：

.. code-block:: cpp

   TEST(StringCmpTest, Demo)
   {
      char* pszCoderZh = "CoderZh";
      wchar_t* wszCoderZh = L"CoderZh";
      std::string strCoderZh = "CoderZh";
      std::wstring wstrCoderZh = L"CoderZh";

      EXPECT_STREQ("CoderZh", pszCoderZh);
      EXPECT_STREQ(L"CoderZh", wszCoderZh);

      EXPECT_STRNE("CnBlogs", pszCoderZh);
      EXPECT_STRNE(L"CnBlogs", wszCoderZh);

      EXPECT_STRCASEEQ("coderzh", pszCoderZh);
      //EXPECT_STRCASEEQ(L"coderzh", wszCoderZh);    不支持

      EXPECT_STREQ("CoderZh", strCoderZh.c_str());
      EXPECT_STREQ(L"CoderZh", wstrCoderZh.c_str());
   }

显示返回成功或失败
****************************************

直接返回成功：SUCCEED();

返回失败：

================  ====================
Fatal assertion   Nonfatal assertion
================  ====================
FAIL();,          ADD_FAILURE();
================  ====================

.. code-block:: cpp

   TEST(ExplicitTest, Demo)
   {
      ADD_FAILURE() << "Sorry"; // None Fatal Asserton，继续往下执行。

      //FAIL(); // Fatal Assertion，不往下执行该案例。

      SUCCEED();
   }

异常检查
****************************************

========================================  =========================================  =================================================
Fatal assertion                           ,Nonfatal assertion                        ,Verifies
========================================  =========================================  =================================================
ASSERT_THROW(statement, exception_type);  ,EXPECT_THROW(statement, exception_type);  ,statement throws an exception of the given type
ASSERT_ANY_THROW(statement);              ,EXPECT_ANY_THROW(statement);              ,statement throws an exception of any type
ASSERT_NO_THROW(statement);               ,EXPECT_NO_THROW(statement);               ,statement doesn't throw any exception
========================================  =========================================  =================================================

例如：

.. code-block:: cpp

   int Foo(int a, int b)
   {
      if (a == 0 || b == 0)
      {
         throw "don't do that";
      }
      int c = a % b;
      if (c == 0)
         return b;
      return Foo(b, c);
   }

   TEST(FooTest, HandleZeroInput)
   {
      EXPECT_ANY_THROW(Foo(10, 0));
      EXPECT_THROW(Foo(0, 5), char*);
   }

Predicate Assertions
****************************************

在使用EXPECT_TRUE或ASSERT_TRUE时，有时希望能够输出更加详细的信息，比如检查一个函数的返回值TRUE还是FALSE时，希望能够输出传入的参数是什么，以便失败后好跟踪。因此提供了如下的断言：

================================  ===========================  ==========================================
Fatal assertion                   ,Nonfatal assertion          ,Verifies
================================  ===========================  ==========================================
ASSERT_PRED1(pred1, val1);        ,EXPECT_PRED1(pred1, val1);  ,pred1(val1) returns true
ASSERT_PRED2(pred2, val1, val2);  ,EXPECT_PRED2(pred2, val1    , val2);,pred2(val1, val2) returns true
...                               ,...                         ,...
================================  ===========================  ==========================================

Google人说了，他们只提供<=5个参数的，如果需要测试更多的参数，直接告诉他们。下面看看这个东西怎么用。

.. code-block:: cpp

   bool MutuallyPrime(int m, int n)
   {
      return Foo(m , n) > 1;
   }

   TEST(PredicateAssertionTest, Demo)
   {
      int m = 5, n = 6;
      EXPECT_PRED2(MutuallyPrime, m, n);
   }

当失败时，返回错误信息：

error: MutuallyPrime(m, n) evaluates to false, where
m evaluates to 5
n evaluates to 6

如果对这样的输出不满意的话，还可以自定义输出格式，通过如下：

==============================================  ===============================================  =========================================
Fatal assertion                                 ,Nonfatal assertion                              ,Verifies
==============================================  ===============================================  =========================================
ASSERT_PRED_FORMAT1(pred_format1, val1);        ,EXPECT_PRED_FORMAT1(pred_format1, val1);        ,pred_format1(val1) is successful
ASSERT_PRED_FORMAT2(pred_format2, val1, val2);  ,EXPECT_PRED_FORMAT2(pred_format2, val1, val2);  ,pred_format2(val1, val2) is successful
...                                             ,...                                             ,...
==============================================  ===============================================  =========================================

用法示例：

.. code-block:: cpp

   testing::AssertionResult AssertFoo(const char* m_expr, const char* n_expr, const char* k_expr, int m, int n, int k) {
      if (Foo(m, n) == k)
         return testing::AssertionSuccess();
      testing::Message msg;
      msg << m_expr << " 和 " << n_expr << " 的最大公约数应该是：" << Foo(m, n) << " 而不是：" << k_expr;
      return testing::AssertionFailure(msg);
   }

   TEST(AssertFooTest, HandleFail)
   {
      EXPECT_PRED_FORMAT3(AssertFoo, 3, 6, 2);
   }

失败时，输出信息：

error: 3 和 6 的最大公约数应该是：3 而不是：2

是不是更温馨呢，呵呵。

浮点型检查
****************************************

===================================  ====================================  ========================================
Fatal assertion                      ,Nonfatal assertion                   ,Verifies
===================================  ====================================  ========================================
ASSERT_FLOAT_EQ(expected, actual);   ,EXPECT_FLOAT_EQ(expected, actual);   ,the two float values are almost equal
ASSERT_DOUBLE_EQ(expected, actual);  ,EXPECT_DOUBLE_EQ(expected, actual);  ,the two double values are almost equal
===================================  ====================================  ========================================

对相近的两个数比较：

===================================  ====================================  ==============================================================================
Fatal assertion                      ,Nonfatal assertion                   ,Verifies
===================================  ====================================  ==============================================================================
ASSERT_NEAR(val1, val2, abs_error);  ,EXPECT_NEAR(val1, val2, abs_error);  ,the difference between val1 and val2 doesn't exceed the given absolute error
===================================  ====================================  ==============================================================================

同时，还可以使用：

.. code-block:: none

   EXPECT_PRED_FORMAT2(testing::FloatLE, val1, val2);
   EXPECT_PRED_FORMAT2(testing::DoubleLE, val1, val2);

Windows HRESULT assertions
****************************************

=====================================  ======================================  ================================
Fatal assertion                        ,Nonfatal assertion                     ,Verifies
=====================================  ======================================  ================================
ASSERT_HRESULT_SUCCEEDED(expression);  ,EXPECT_HRESULT_SUCCEEDED(expression);  ,expression is a success HRESULT
ASSERT_HRESULT_FAILED(expression);     ,EXPECT_HRESULT_FAILED(expression);     ,expression is a failure HRESULT
=====================================  ======================================  ================================

例如：

.. code-block:: cpp

   CComPtr shell;
   ASSERT_HRESULT_SUCCEEDED(shell.CoCreateInstance(L"Shell.Application"));
   CComVariant empty;
   ASSERT_HRESULT_SUCCEEDED(shell->ShellExecute(CComBSTR(url), empty, empty, empty, empty));

类型检查
****************************************

类型检查失败时，直接导致代码编不过，难得用处就在这？看下面的例子：

.. code-block:: cpp

   template <typename T> class FooType {
   public:
      void Bar() { testing::StaticAssertTypeEq<int, T>(); }
   };

   TEST(TypeAssertionTest, Demo)
   {
      FooType<bool> fooType;
      fooType.Bar();
   }

总结
****************************************

本篇将常用的断言都介绍了一遍，内容比较多，有些还是很有用的。要真的到写案例的时候，也行只是一两种是最常用的，现在时知道有这么多种选择，以后才方便查询。