go test ./... does not detect tests in submodules of multimodule projects

[cyrusv]

What version of Go are you using (go version)?

1.20.1

Does this issue reproduce with the latest release?

Yes

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

amd64

What did you do?

go test ./... documentation specifies that it will find all subpackages. Documentation leads to believe that all test files will be executed. However, test files in a submodule of a multi-module project are ignored.

This is especially shocking when your CICD is counting on go test ./..., and you add a v2 submodule.

People work around it like this: https://stackoverflow.com/questions/61163306/running-go-test-in-parent-directory-of-multiple-go-modules

Either this is a bug that should be fixed (happy to open a PR with some guidance), or the documentation should be updated to specify the expected behavior in submodule/multimodule case.

[seankhliao]

Duplicate of #27957