gtest-断言

一、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。

二、示例

// 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：

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）

<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：

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：

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：

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：

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

三、布尔值检查

Fatal assertion	Nonfatal assertion	Verifies
ASSERT_TRUE(condition);	EXPECT_TRUE(condition);	condition is true
ASSERT_FALSE(condition);	EXPECT_FALSE(condition);	condition is false

四、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

五、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：

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());
}

六、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();

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();
}

七、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：

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*);
}

八、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。

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：

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

九、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：

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

十、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：

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

十一、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：

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

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

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