}

	// Use ReadFrom to read in some data.
	r := &emptyThenNonEmptyReader{r: strings.NewReader("abcd"), n: 100}
	n2, err := w.ReadFrom(r)
	if n2 != 0 || err != io.ErrNoProgress {
		t.Fatalf("buf.Bytes() returned (%v, %v), want (0, io.ErrNoProgress)", n2, err)
	}
}

type readFromWriter struct {
	buf           []byte
	writeBytes    int
	readFromBytes int
}