How to hide stack frames in a subclass of TestCase?

Question

I want to add a custom assert method to a subclass of TestCase . I tried to copy my implementation from the unittest module unittest that it would match the behavior of the regular TestCase as much as possible. (I would rather just delegate self.assertEqual() , but this causes even more upstream noise, see below.) The unittest module seems to automatically hide some of the internal details of its implementation when reporting failed statements.

 import unittest class MyTestCase(unittest.TestCase): def assertLengthIsOne(self, sequence, msg=None): if len(sequence) != 1: msg = self._formatMessage(msg, "length is not one") raise self.failureException(msg) class TestFoo(MyTestCase): seq = (1, 2, 3, 4, 5) def test_stock_unittest_assertion(self): self.assertEqual(len(self.seq), 1) def test_custom_assertion(self): self.assertLengthIsOne(self.seq) unittest.main() 

The result of this as such:

 amoe@vuurvlieg $ python unittest-demo.py FF ====================================================================== FAIL: test_custom_assertion (__main__.TestFoo) ---------------------------------------------------------------------- Traceback (most recent call last): File "unittest-demo.py", line 16, in test_custom_assertion self.assertLengthIsOne(self.seq) File "unittest-demo.py", line 7, in assertLengthIsOne raise self.failureException(msg) AssertionError: length is not one ====================================================================== FAIL: test_stock_unittest_assertion (__main__.TestFoo) ---------------------------------------------------------------------- Traceback (most recent call last): File "unittest-demo.py", line 13, in test_stock_unittest_assertion self.assertEqual(len(self.seq), 1) AssertionError: 5 != 1 ---------------------------------------------------------------------- Ran 2 tests in 0.000s FAILED (failures=2) 

Note that the custom assert method invokes a stack trace with two frames, one inside the method itself, while the unittest stock unittest has only one frame, the corresponding line in the user code. How can I apply this behavior when hiding frames to my own method?

Answer 1

This question was answered by Peter Otten at comp.lang.python .

Move MyTestCase to a separate module and define the global variable __unittest = True .

 $ cat mytestcase.py import unittest __unittest = True class MyTestCase(unittest.TestCase): def assertLengthIsOne(self, sequence, msg=None): if len(sequence) != 1: msg = self._formatMessage(msg, "length is not one") raise self.failureException(msg) $ cat mytestcase_demo.py import unittest from mytestcase import MyTestCase class TestFoo(MyTestCase): seq = (1, 2, 3, 4, 5) def test_stock_unittest_assertion(self): self.assertEqual(len(self.seq), 1) def test_custom_assertion(self): self.assertLengthIsOne(self.seq) if __name__ == "__main__": unittest.main() $ python mytestcase_demo.py FF ====================================================================== FAIL: test_custom_assertion (__main__.TestFoo) ---------------------------------------------------------------------- Traceback (most recent call last): File "mytestcase_demo.py", line 11, in test_custom_assertion self.assertLengthIsOne(self.seq) AssertionError: length is not one ====================================================================== FAIL: test_stock_unittest_assertion (__main__.TestFoo) ---------------------------------------------------------------------- Traceback (most recent call last): File "mytestcase_demo.py", line 8, in test_stock_unittest_assertion self.assertEqual(len(self.seq), 1) AssertionError: 5 != 1 ---------------------------------------------------------------------- Ran 2 tests in 0.000s FAILED (failures=2) $