c++ - 枚举类的 GoogleTest 测试错误打印

Question

我正在使用 GoogleTest 1.7.0 版来测试我的 C++ 应用程序。我有一个枚举定义如下

namespace MyNamespace {
    enum class MyEnum {
        MyEnumValue,
        MyEnumValue2
    }
}

GoogleTest 错误地打印它的值，导致测试失败时出现此错误消息:

Value of: MyClass.MyMethodThatReturnsEnum()

Actual: 4-byte object

Expected: MyEnum::MyEnumValue

Which is: 4-byte object <02-00 00-00>

删除 class 关键字会生成带有枚举实际值的正确错误消息。这是 GoogleTest 的已知行为/错误吗？有办法解决这个问题吗？

MyClass my_class;

EXPECT_EQ(MyEnum::MyEnumValue, my_class.MyMethodThatReturnsEnum());

Answer 1

当您在 enum class MyEnum 中定义常量时，您将它们定义为对象属于用户定义类型 MyEnum，其中没有隐式转换任何整数类型。这是 enum class 的目标，但它不是让 Googletest 假设您想要 MyEnum 类型的对象自动为了插入输出而转换为整数类型流，如果您选择使该类型成为 enum class 而不仅仅是一个枚举。

所以您观察到的不是 Googletest 错误。它只是 Googletest 使用其某种类型的用户定义对象的回退表示 T for which

std::ostream & operator<<(std::ostream &, T const &);

未定义。

如果你想查看enum class MyEnum类型对象的整数值出现在 Googletest 的测试诊断中，您至少有两种方法。

一种方法是简单地将测试应用于对象的基础积分值，如:

ma​​in.cpp(1)

#include <gtest/gtest.h>
#include <type_traits>

enum class MyEnum {
    Value,
    Value2
};

auto as_integral(MyEnum me)
-> std::underlying_type<MyEnum>::type
{
    return static_cast<std::underlying_type<MyEnum>::type>(me);
}

TEST(foo,bar)
{
    EXPECT_EQ(as_integral(MyEnum::Value),as_integral(MyEnum::Value2));
}

int main(int argc, char **argv) {
    ::testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}

编译、链接和运行:

$ g++ -std=c++11 -Wall -Wextra -o gtester main.cpp -lgtest  -lpthread
$ ./gtester
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from foo
[ RUN      ] foo.bar
main.cpp:17: Failure
Expected equality of these values:
  as_integral(MyEnum::Value)
    Which is: 0
  as_integral(MyEnum::Value2)
    Which is: 1
[  FAILED  ] foo.bar (0 ms)
[----------] 1 test from foo (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] foo.bar

 1 FAILED TEST

另一种更好的方法是为 Googletest 提供以下定义:

std::ostream & operator<<(std::ostream &, MyEnum const &);

适合你。然后 Googletest 将在其诊断中使用它，如:

ma​​in.cpp(2)

#include <gtest/gtest.h>
#include <type_traits>
#include <ostream>

enum class MyEnum {
    Value,
    Value2
};

auto as_integral(MyEnum me)
-> std::underlying_type<MyEnum>::type
{
    return static_cast<std::underlying_type<MyEnum>::type>(me);
}

std::ostream & operator<<(std::ostream & out, MyEnum me)
{
    return out << as_integral(me);
}

TEST(foo,bar)
{
    EXPECT_EQ(MyEnum::Value,MyEnum::Value2);
}

int main(int argc, char **argv) {
    ::testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}

编译、链接和运行:

$ g++ -std=c++11 -Wall -Wextra -o gtester main.cpp -lgtest  -lpthread
$ ./gtester
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from foo
[ RUN      ] foo.bar
main.cpp:23: Failure
Expected equality of these values:
  MyEnum::Value
    Which is: 0
  MyEnum::Value2
    Which is: 1
[  FAILED  ] foo.bar (0 ms)
[----------] 1 test from foo (0 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (0 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] foo.bar

 1 FAILED TEST