str, err := cw.WriteTree(tmpdir, log.New(os.Stdout, "", 0))
c.Check(err, IsNil)
c.Check(str, Equals, ". acbd18db4cc2f85cedef654fccc4a4d8+3 0:3:file1.txt\n")
str, err := cw.WriteTree(tmpdir, log.New(os.Stdout, "", 0))
c.Check(err, IsNil)
c.Check(str, Equals, ". acbd18db4cc2f85cedef654fccc4a4d8+3 0:3:file1.txt\n")