Antoine and Éric: Thank you for the reviews and suggestions.

> Why the "__unittest" variable?

I added the "__unittest" variable after read issue 7815 and the related
changeset: http://hg.python.org/cpython/rev/2858cae540e4/

See also:
- http://stackoverflow.com/questions/12583015/how-can-i-hide-my-stack-frames-in-a-testcase-subclass
- https://github.com/nose-devs/nose2/pull/28/files

However, without the variable tracebacks are still clear:

$ pyunit -v
test_acc (test_bar.TestAcc) ... ok
test_acc_negative (test_bar.TestAccNegative) ... ok
test_mul (test_foo.TestMul) ... ok
test_mul_negative (test_foo.TestMulNegative) ... ok
test_mul (test_baz.TestMul) ... FAIL

======================================================================
FAIL: test_mul (test_baz.TestMul)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/berker/hacking/cpython/test_baz.py", line 12, in test_mul
    self.assertEqual(3, mul(2, 2))
AssertionError: 3 != 4

----------------------------------------------------------------------
Ran 5 tests in 0.002s

FAILED (failures=1)

> Also, it would be better to make unittest's API more flexible, rather
> than manually tweaking sys.argv to enable discovery.

You're right. Something like that? unittest.main(discover=True)

> About the script: can’t it be as simple as runpy.run_module?

I will try that, thanks.