return s
}

// Fill buf through n writes of byte slice fub.
// The initial contents of buf corresponds to the string s;
// the result is the final contents of buf returned as a string.
func fillBytes(t *testing.T, testname string, buf *Buffer, s string, n int, fub []byte) string {
	check(t, testname+" (fill 1)", buf, s)
	for ; n > 0; n-- {
		m, err := buf.Write(fub)
		if m != len(fub) {