b.WriteString("0")                         // easy
	b.WriteString("123456")                    // still easy
	b.WriteString("7890")                      // easy after flush
	b.WriteString("abcdefghijklmnopqrstuvwxy") // hard
	b.WriteString("z")
	if err := b.Flush(); err != nil {
		t.Error("WriteString", err)
	}
	s := "01234567890abcdefghijklmnopqrstuvwxyz"
	if buf.String() != s {