[pull request] Fix broken test, simplify test asserts and facilitate running tests

[Magnus Ihse Bursie <magnus ihse net>]

Hi,

I'd like to help contribute with more and better unit tests for Meld. As 
a start, I've created a small patch that fixes so the current test suite 
passes without failures, and makes it slightly more inviting to run tests.

I have created a pull request on github: 
https://github.com/GNOME/meld/pull/6. This is based on the GNOME github 
mirror of Meld, https://github.com/GNOME/meld. Does this seem like a 
good way to contribute, or do you want me to mail a patch to the list 
instead?

/Magnus