Fix unit tests

[datagutten]

The tests currently use an empty string or the default value for checking exception message which means empty message. The message is not empty and causes the tests to fail. I changed this to null so the message is not checked and those tests pass.

[codecov-io]

Codecov Report

Merging #345 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #345   +/-   ##
=========================================
  Coverage     92.11%   92.11%           
  Complexity      760      760           
=========================================
  Files            21       21           
  Lines          1762     1762           
=========================================
  Hits           1623     1623           
  Misses          139      139

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[jrfnl]

Wouldn't it make more sense to let Composer sort out the PHPUnit version on every build ?
That would make the Travis script much simpler and more stable.

[rmccue]

Thanks so much for this pull request and apologies for the delay. I've rolled these tests into #351 to also update the domain name; will aim to merge that.