if string(m) != expect {
		t.Errorf("drop: expected %q got %q", expect, m)
	}

	// 6. Invalid rune
	invalidRune := func(r rune) rune {
		return utf8.MaxRune + 1
	}
	m = Map(invalidRune, []byte("x"))
	expect = "\uFFFD"
	if string(m) != expect {
		t.Errorf("invalidRune: expected %q got %q", expect, m)
	}
}

func TestToUpper(t *testing.T) { runStringTests(t, ToUpper, "ToUpper", upperTests) }