// zeroes
	_, err := NewReader(bytes.NewReader(b), size)
	if err != ErrFormat {
		t.Errorf("zeroes: error=%v, want %v", err, ErrFormat)
	}

	// repeated directoryEndSignatures
	sig := make([]byte, 4)
	binary.LittleEndian.PutUint32(sig, directoryEndSignature)
	for i := 0; i < size-4; i += 4 {
		copy(b[i:i+4], sig)
	}
	_, err = NewReader(bytes.NewReader(b), size)
	if err != ErrFormat {

			switch j {
			case 0:
				tr = NewReader(&reader{strings.NewReader(v.input)})
				s1, s2 = "io.Reader", "auto"
			case 1:
				tr = NewReader(&reader{strings.NewReader(v.input)})
				s1, s2 = "io.Reader", "manual"
			case 2:
				tr = NewReader(&readSeeker{strings.NewReader(v.input)})
				s1, s2 = "io.ReadSeeker", "auto"
			case 3:
				tr = NewReader(&readSeeker{strings.NewReader(v.input)})

	var with, withOut nErr
	with.n, with.err = io.Copy(discard, NewReader(nil))
	withOut.n, withOut.err = io.Copy(discard, justReader{NewReader(nil)})
	if with != withOut {
		t.Errorf("behavior differs: with = %#v; without: %#v", with, withOut)
	}
}

// tests that Len is affected by reads, but Size is not.
func TestReaderLenSize(t *testing.T) {
	r := NewReader([]byte("abc"))
	io.CopyN(io.Discard, r, 1)
	if r.Len() != 2 {