This is what I see in my tree:

E
======================================================================
ERROR: test_os (unittest.loader.ModuleImportFailure)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/robertc/work/cpython/Lib/unittest/case.py", line 58, in testPartExecutor
    yield
  File "/home/robertc/work/cpython/Lib/unittest/case.py", line 577, in run
    testMethod()
  File "/home/robertc/work/cpython/Lib/unittest/loader.py", line 36, in testFailure
    raise exception
ImportError: Failed to import test module: test_os
Traceback (most recent call last):
  File "/home/robertc/work/cpython/Lib/unittest/loader.py", line 146, in loadTestsFromName
    module = __import__(module_name)
  File "/home/robertc/work/cpython/Lib/test/test_os.py", line 5, in <module>
    import broken
ImportError: No module named 'broken'