writeTests[1].Data = nil
	}()

	// write a zip file
	buf := new(bytes.Buffer)
	existingData := []byte{1, 2, 3, 1, 2, 3, 1, 2, 3}
	n, _ := buf.Write(existingData)
	w := NewWriter(buf)
	w.SetOffset(int64(n))

	for _, wt := range writeTests {
		testCreate(t, w, &wt)
	}

	if err := w.Close(); err != nil {
		t.Fatal(err)
	}

	// read it back