if n, err := r.WriteTo(w); err != nil || n != int64(len(input)) {
		t.Fatalf("r.WriteTo(w) = %d, %v, want %d, nil", n, err, len(input))
	}

	for i, val := range w.Bytes() {
		if val != input[i] {
			t.Errorf("after write: out[%d] = %#x, want %#x", i, val, input[i])
		}
	}
}

type errorWriterToTest struct {
	rn, wn     int
	rerr, werr error
	expected   error
}