// Invalid runes, including negative ones, should be written as the
	// replacement character.
	for _, r := range []rune{-1, utf8.MaxRune + 1} {
		var buf strings.Builder
		w := NewWriter(&buf)
		w.WriteRune(r)
		w.Flush()
		if s := buf.String(); s != "\uFFFD" {
			t.Errorf("WriteRune(%d) wrote %q, not replacement character", r, s)
		}
	}
}

func TestReadStringAllocs(t *testing.T) {