How to run existing tests on a python lib cloned form github?

I downloaded a python lib from github. I made a few changes to the source code. I wanted to run the tests that it contained to see if I didn't break anything.

There is a tests directory at the top level along with a directory - xyz

Now this xyz package is being imported in a file inside the tests directory.

On running the test, I get an error saying:

ImportError: No module named 'xyz'

What should I do to run the tests ?

Here is the lib: http://ift.tt/1F68bf7