}
	var Y *Int
	if y != nil {
		Y = new(Int)
	}

	D := new(Int).GCD(X, Y, a, b)
	if D.Cmp(d) != 0 {
		t.Errorf("GCD(%s, %s, %s, %s): got d = %s, want %s", x, y, a, b, D, d)
	}
	if x != nil && X.Cmp(x) != 0 {
		t.Errorf("GCD(%s, %s, %s, %s): got x = %s, want %s", x, y, a, b, X, x)
	}
	if y != nil && Y.Cmp(y) != 0 {
		t.Errorf("GCD(%s, %s, %s, %s): got y = %s, want %s", x, y, a, b, Y, y)
	}

		fuzzArg = []string{"-test.fuzzcachedir=" + fuzzCacheDir}
	}
	coverdirArg := []string{}
	addToEnv := ""
	if cfg.BuildCover {
		gcd := filepath.Join(a.Objdir, "gocoverdir")
		if err := sh.Mkdir(gcd); err != nil {
			// If we can't create a temp dir, terminate immediately
			// with an error as opposed to returning an error to the
			// caller; failed MkDir most likely indicates that we're