The nose tools wrap python's unittest module, and unfortunately it appears assertIs wasn't introduced until 2.7. As a result, with Python2.6 this test gets an ImportError, and the nose test claims:

```
ERROR: Failure: AttributeError ('module' object has no attribute 'test_legend')
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/virtualenv/python2.6/lib/python2.6/site-packages/nose/loader.py", line 402, in loadTestsFromName
    module = resolve_name(addr.module)
  File "/home/travis/virtualenv/python2.6/lib/python2.6/site-packages/nose/util.py", line 321, in resolve_name
    obj = getattr(obj, part)
AttributeError: 'module' object has no attribute 'test_legend'
```