This is not something that is specific to unittest.  In Python, if you call a generator function *it returns a generator-iterator*.  Unless you *do* something with the the iterator, nothing else happens.  This is true in *any* python code.  

Unittest calls whatever test method you define, and handles (reports) the exceptions that result from that call.  That's the fundamental design of unittest.  Your generator test method does not raise any exceptions when called, therefore the test passed.