I'm afraid you need to also add this dependency to .travis.yml, or make the tests pass on 2.6 when unittest2 is not available.

Something like this should work:

```
install:
    - pip install . --use-mirrors
    - test $TRAVIS_PYTHON_VERSION = "2.6" && pip install unittest2 --use-mirrors
```

Personally, I'm fine with making unittest2 a mandatory dependency on Python 2.6.