"unittest discover" does add some directories to sys.path

later some modules can not work with modified sys.path

Here module `pdb` is trying to import standard module `cmd` but does import `cmd` module from `tests` directory:

"unittest discover" should not modify sys.path in any way.

http://dpaste.com/2RYV8E0

$ mkdir /tmp/t
$ cd /tmp/t
$ mkdir tests
$ mkdir tests/cmd
$ touch tests/cmd/__init__.py
$ echo "import pdb" > tests/test_nothing.py
$ python -m unittest discover tests
E
======================================================================
ERROR: test_nothing (unittest.loader.ModuleImportFailure)
----------------------------------------------------------------------
ImportError: Failed to import test module: test_nothing
Traceback (most recent call last):
  File "/usr/lib/python2.7/unittest/loader.py", line 254, in _find_tests
    module = self._get_module_from_name(name)
  File "/usr/lib/python2.7/unittest/loader.py", line 232, in _get_module_from_name
    __import__(name)
  File "/tmp/t/tests/test_nothing.py", line 1, in <module>
    import pdb
  File "/usr/lib/python2.7/pdb.py", line 59, in <module>
    class Pdb(bdb.Bdb, cmd.Cmd):
AttributeError: 'module' object has no attribute 'Cmd'


----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (errors=1)

It did that because you did not specify a top level directory. Without that, the cwd is not on the path and that breaks many environments.

We should probably document it better. The workaround for your needs is to either just run 'unittest discover', or run 'unittest discover tests -t .', not 'unittest discover tests'.

The behaviour is however something I believe to be correct and essential to most user experiences.

This is alluded to in the "caution" under https://docs.python.org/3/library/unittest.html#test-discovery

But the workaround is not explained.