Unit-test/Travis CI: cleaner log

[jbesomi]

The current Travis CI log isn't particularly beautiful, example.

This task consists of cleaning the log output of travis CI by mainly improving the unit-tests files.

Also, sometimes the Travis CI does not fail even if some errors are raised, see example below at line 576 for instance (`raise IOError(Errors.E050.format(name=name))). This should also investigate further. In this case, we may want the job to fail rather than pass?