gtest-system-error.hpp

#include <gtest/gtest.h>
#include <system_error>
#define ASSERT_SYSTEM_ERROR(statement, error_code) \
    ASSERT_THROW({\
        try { \
          GTEST_SUPPRESS_UNREACHABLE_CODE_WARNING_BELOW_(statement); \
        } \
        catch(const std::system_error &exception) {\
            ASSERT_EQ(error_code, exception.code());\
            throw;\
        }\
    }, std::system_error)

#define EXPECT_SYSTEM_ERROR(statement, error_code) \
    EXPECT_THROW({\
        try { \
          GTEST_SUPPRESS_UNREACHABLE_CODE_WARNING_BELOW_(statement); \
        } \
        catch(const std::system_error &exception) {\
            EXPECT_EQ(error_code, exception.code());\
            throw;\
        }\
    }, std::system_error)

sample.cpp

#include <gtest/gtest.h>
#include "gtest-system-error.hpp"

#include <thread>

// Example of exception took from
// http://en.cppreference.com/w/cpp/error/system_error

TEST(Test,TestPassed)
{
  EXPECT_SYSTEM_ERROR(std::thread().detach(), std::make_error_code(std::errc::invalid_argument));
}
TEST(Test,TestFailed)
{
  EXPECT_SYSTEM_ERROR(std::thread().detach(), std::make_error_code(std::errc::io_error));
}

On my test environment the Test.TestFailed report error twice. Why?