Fix test failure on Ubuntu

I found that some unit test fails on Ubuntu (as I mentioned in #4).  This pull request fixes those test failures.

We can see the test result for this pull request on Travis CI here: [![Build Status](https://travis-ci.org/xKerman/uxu.svg?branch=fix-test-failure)](https://travis-ci.org/xKerman/uxu/builds/28120090)