Question

我正在尝试将std::chrono类型用于Google测试。我的第一种方法是在命名空间PrintTo中为nanoseconds定义std::chrono，但不幸的是it is undefined behavior to add declarations or definitions to namespace std or to any namespace nested within std。以下代码演示了该想法。

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

namespace std::chrono {

void PrintTo(nanoseconds ns, std::ostream* os) // UB
{
    *os << ns.count() << " nanoseconds ";
}

}

namespace {

struct MyTest : ::testing::Test{
};

TEST_F(MyTest, PrintingTest)
{
    using namespace testing;
    using namespace std::chrono_literals;
    ASSERT_THAT(1ns, Eq(2ns));
}

}

如果定义了std::chrono::PrintTo，它将打印：

Value of: 1ns
Expected: is equal to 2 nanoseconds 
  Actual:

如果未定义std::chrono::PrintTo，它将通过默认的字节打印机进行打印：

Value of: 1ns
Expected: is equal to 8-byte object <02-00 00-00 00-00 00-00>
  Actual:

用Google测试为std::chrono类型定义打印机的惯用方式是什么？

Answer 1

您可以按如下所示重载chrono类型的std :: ostream运算符：

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

std::ostream& operator<<(std::ostream& os, const ::std::chrono::nanoseconds& ns) 
{
  return os << ns.count() << " nanoseconds ";
}

namespace {

struct MyTest : ::testing::Test{
};

TEST_F(MyTest, PrintingTest)
{
    using namespace testing;
    using namespace std::chrono_literals;
    ASSERT_EQ(1ns, 2ns);
}

}

输出应符合预期：

error:       Expected: 1ns
      Which is: 1 nanoseconds
To be equal to: 2ns
      Which is: 2 nanoseconds
[  FAILED  ] MyTest.PrintingTest (0 ms)

如何使用Google Test打印std :: chrono类型？

1 个答案: