" || err != nil {   t.Fatalf("want %q got %q, err=%v", "abc", string(p[0:0]), err)  }  if s, err := buf.Peek(0); string(s) != "d" || err != nil {   t.Fatalf("want %q got %q, err=%v", "d", string(s), err)  }  if s, err := buf.Peek(0); string(s) != "d