You need to make sure your PYTHONPATH is set correctly so the command-line interpreter can find your packages, or run your test cases from within Eclipse Pydev. __Update__: Another option: running your tests using [nose](http://pypi.python.org/pypi/nose) might make things a bit easier, since it can auto-discover packages and test cases.

If your project is laid out like so:

 /home/user/dev/
 src/pkg1/
 mod1.py

 test/
 mod1_test.py

Use: `PYTHONPATH=$HOME/dev/src python test/mod1_test.py`. I'd also recommend using [`distribute`](http://pypi.python.org/pypi/distribute) and [`virtualenv`](http://pypi.python.org/pypi/virtualenv) to set up your project for development.