玩转Google开源C++单元测试框架Google Test系列(gtest)之二 – 断言

作者：CoderZh（CoderZh的技术博客 - 博客园）
微博：http://t.sina.com.cn/coderzh
出处：http://coderzh.cnblogs.com

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.kgdb.info/linuxdev/gtest_6/）

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

是不是更温馨呢，呵呵。

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));