continue
			}
		}

		// If we were unable to read anything out of the archive don't
		// bother trying to roundtrip it.
		if len(files) == 0 {
			return
		}

		w := NewWriter(io.Discard)
		for _, f := range files {
			ww, err := w.CreateHeader(f.header)
			if err != nil {
				t.Fatalf("unable to write previously parsed header: %s", err)
			}
			if _, err := ww.Write(f.content); err != nil {

		n   int64
		err error
	}
	type justReader struct {
		io.Reader
	}
	type justWriter struct {
		io.Writer
	}
	discard := justWriter{io.Discard} // hide ReadFrom

	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)
	}
}