Tests passing locally, but not on TravisCI - Cause is unknown

Cause is unknown, at least to me...

I have a bunch of tests which are working great on my local machine, but wont pass on TravisCI. This is happening on an open source package stored on Github which you can easily check out.

The failed builds can be seen here: https://travis-ci.org/dugajean/pouch/builds/472391121
And the tests can be found here: https://github.com/dugajean/pouch/tree/master/tests

The errors/exceptions thrown on TravisCI simply don't happen locally. What I get locally is:

OK (15 tests, 22 assertions)

I simply can't see what I could be doing wrong. Help would be highly appreciated.