var z *Reader
	var err error
	var raw []byte
	if zt.Source != nil {
		rat, size := zt.Source()
		z, err = NewReader(rat, size)
		raw = make([]byte, size)
		if _, err := rat.ReadAt(raw, 0); err != nil {
			t.Errorf("ReadAt error=%v", err)
			return
		}
	} else {
		path := filepath.Join("testdata", zt.Name)
		if zt.Obscured {
			tf, err := obscuretestdata.DecodeToTempFile(path)
			if err != nil {

	for i := 0; i < len(all); i++ {
		for j := 0; j < len(all)-i; j++ {
			buf := make([]byte, j)
			n, err := b.ReadAt(buf, int64(i))
			if err != nil || n != len(buf) {
				t.Errorf("ReadAt(%d, %d) = %d, %v; want %d, nil", i, j, n, err, len(buf))
			}
			if !bytes.Equal(buf, all[i:i+j]) {
				t.Errorf("ReadAt(%d, %d) = %q; want %q", i, j, buf, all[i:i+j])
			}
		}
	}
}