if !strings.HasPrefix(output, want) {
		t.Fatalf("output does not start with %q:\n%s", want, output)
	}
}

func TestNoHelperGoroutines(t *testing.T) {
	output := runTestProg(t, "testprog", "NoHelperGoroutines")
	matches := regexp.MustCompile(`goroutine [0-9]+ \[`).FindAllStringSubmatch(output, -1)
	if len(matches) != 1 || matches[0][0] != "goroutine 1 [" {
		t.Fatalf("want to see only goroutine 1, see:\n%s", output)
	}