cmd/go: go test reports module missing when no test files in the cwd

[davecheney]

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

$go version
go version devel +964fe4b80f Thu Apr 4 00:26:24 2019 +0000 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

% mkdir ~/devel/mod.a && cd ~/devel/mod.a
% go mod init github.com/davecheney/mod.a
% go test

What did you expect to see?

can't load package: package github.com/davecheney/mod.a: no Go files in /Users/dfc/devel/mod.a

What did you see instead?

can't load package: package github.com/davecheney/mod.a: unknown import path "github.com/davecheney/mod.a": cannot find module providing package github.com/davecheney/mod.a

[bcmills]

I feel like this is a duplicate but I can't find it right now.

CC @jayconrod

[bcmills]

Duplicate of #27122