if err := os.Mkdir(dir, 0777); err != nil {
		t.Fatal(err)
	}
	defer tdmu.Unlock()
	return dir
}

// TestCoverWithToolExec runs a set of subtests that all make use of a
// "-toolexec" wrapper program to invoke the cover test executable
// itself via "go test -cover".
func TestCoverWithToolExec(t *testing.T) {
	testenv.MustHaveExec(t)

	toolexecArg := "-toolexec=" + testcover(t)