Could you provide a more complete recipe for reproducing the problem,
please?  I created a test_foo.py containing 'import blert', and running
python -m unittest test_foo does not mask the import error for blert in
loadTestsFromName:

...
  File "/usr/lib/python2.6/unittest.py", line 576, in loadTestsFromName
    module = __import__('.'.join(parts_copy))
  File "test_foo.py", line 1, in <module>
    import blert
ImportError: No module named blert