src/cmd/go/testdata/script/test_match_only_subtests.txt

# Matches only subtests
go test -run Test/Sub standalone_sub_test.go
! stdout '^ok.*\[no tests to run\]'
! stderr '^ok.*\[no tests to run\]'
stdout '^ok'

-- standalone_sub_test.go --
package standalone_sub_test

import "testing"

func Test(t *testing.T) {
	t.Run("Sub", func(t *testing.T) {})
}