去测试`-parallel`与`-test.parallel`哪个标志优先？

Question

Difference between go test's two flags -parallel and -test.parallel and which flag gets precedence?

-parallel n
            Allow parallel execution of test functions that call t.Parallel.
            The value of this flag is the maximum number of tests to run
            simultaneously; by default, it is set to the value of GOMAXPROCS.
            Note that -parallel only applies within a single test binary.
            The 'go test' command may run tests for different packages
            in parallel as well, according to the setting of the -p flag
            (see 'go help build').

Above documentation says that the number of tests that are run in parallel are equal to GOMAXPROCS if nothing is provided, but the behavior is not like that for me. Because I am running tests on a machine that has only 4 cores. But for me 8 tests run in parallel, so the behavior is more like following:

-test.parallel int
        maximum test parallelism (default 8)

So what is the difference between the two? When to use which flag.

More Information

I am running all tests on a single package which has 9 tests, all of them are run parallely and all those exist in single test function.

Answer 1

The -test. flags are generated by go test command. The go test command produces a pkg.test binary on the fly and runs it with modified arguments. All the recognized arguments passed to go test will be converted. So, in your case: -parallel n becomes -test.parallel n.

So this command:

go test -parallel 6

creates:

pkg.test -test.parallel 6