testing: invalid `testing.go:1343: test executed panic(nil) or runtime.Goexit: subtest may have called FailNow on a parent test` error

[alexbrainman]

$ go version

I use play.golang.org website.

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

I use play.golang.org website.

What did you do?

I run this test

https://go.dev/play/p/BtIQcyQJYxR

What did you expect to see?

I expected to see this

=== RUN   TestRunFatal
=== RUN   TestRunFatal/Alex
    prog_test.go:11: Alex
--- FAIL: TestRunFatal (0.00s)
    --- FAIL: TestRunFatal/Alex (0.00s)
FAIL

Program exited.

This output is from slightly modified version of my test

https://go.dev/play/p/QeGIM_xxA4E

What did you see instead?

I see this

=== RUN   TestRunFatal
=== RUN   TestRunFatal/Alex
=== CONT  TestRunFatal
    prog_test.go:11: Alex
=== CONT  TestRunFatal/Alex
    testing.go:1343: test executed panic(nil) or runtime.Goexit: subtest may have called FailNow on a parent test
--- FAIL: TestRunFatal (0.00s)
    --- FAIL: TestRunFatal/Alex (0.00s)
FAIL

Program exited.

Perhaps I don't understand how tests work. But I was surprised and confused by the

    testing.go:1343: test executed panic(nil) or runtime.Goexit: subtest may have called FailNow on a parent test

error message. I also tried reading testing.FailNow documentation at

https://pkg.go.dev/testing#T.FailNow

The documentation talks about goroutines, but I don't have any goroutines in my test.

Thank you for investigating this.

Alex

[qiulaidongfeng]

Document in https://pkg.go.dev/testing#T.Run
Run runs f as a subtest of t called name. It runs f in a separate goroutine and blocks until f returns or calls t.Parallel to become a parallel test.

Document in https://pkg.go.dev/testing#T.Fatal
Fatal is equivalent to Log followed by FailNow.

https://go.dev/play/p/BtIQcyQJYxR A new goroutine is opened in the code t.Run() of. In this goroutine, TestRunFatal's t.Fatal() calls TestRunFatal's t.FailNow(). This is expected behavior.

[alexbrainman]

This is expected behavior.

Maybe you are correct @qiulaidongfeng .

Alex

[mknyszek]

That's right, this behavior is expected. The test captures t from the parent test and fails it from the subtest, which isn't allowed (because it's not on that test's goroutine).

[mknyszek]

On the topic of error messages and documentation, I think this could probably be a bit clearer, or have an example. I wonder if any of the go.dev tutorials point this out.