if err != nil {
		t.Fatal(err)
	}
	if got, want := strings.TrimSpace(string(out)), "good"; got != want {
		t.Errorf("output = %q; want %q", got, want)
	}
}

func TestEnvNULCharacter(t *testing.T) {
	if runtime.GOOS == "plan9" {
		t.Skip("plan9 explicitly allows NUL in the environment")
	}
	cmd := helperCommand(t, "echoenv", "FOO", "BAR")