func (w *writeCountingDiscard) Write(p []byte) (int, error) {
	*w++
	return len(p), nil
}

type negativeReader int

func (r *negativeReader) Read([]byte) (int, error) { return -1, nil }

func TestNegativeRead(t *testing.T) {
	// should panic with a description pointing at the reader, not at itself.
	// (should NOT panic with slice index error, for example.)
	b := NewReader(new(negativeReader))
	defer func() {