t.Fatalf("creating covdir: %v", err)
	}
	large := fmt.Sprintf("%07999d", 0)
	cmd = testenv.Command(t, exepath, "1", "2", "3", large)
	cmd.Dir = covdir
	cmd.Env = append(os.Environ(), "GOCOVERDIR="+covdir)
	b, err = cmd.CombinedOutput()
	if err != nil {
		t.Logf("## run output:\n%s", b)
		t.Fatalf("build error: %v", err)
	}

	vis := &visitor{}