exception stack depth not restricted to relevant modules

[Luke Diamand]

Hi!

I'm just playing around with testtools trying to understand what I need to do to use them.

One thing I noticed is that when a test fails, I get the complete interpreter stack in the exception:

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/testtools/runtest.py", line 169, in _run_user
    return fn(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 499, in _run_test_method
    return self._get_test_method()()
  File "./test-tt.py", line 17, in test_foo
    self.assertEqual(1,0)
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 268, in assertEqual
    self.assertThat(observed, matcher)
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 345, in assertThat
    % (matchee, matcher, mismatch.describe()))
AssertionError: Match failed. Matchee: "0"
Matcher: Equals(1)
Difference: 1 != 0

But most of that information is irrelevant, and I don't want to be trawling through it trying to work out what's going on.

In "unittest", it gets truncated to just the relevant parts:

Traceback (most recent call last):
  File "./test.py", line 15, in test_foo
    self.assertEqual(1,0)
AssertionError: 1 != 0

It looks like unittest has some code to strip out the junk, in the shape of functions _is_relevant_tb_levels() and _count_relevant_tb_levels().

I started looking to see where this could be fixed but couldn't see quite the cleanest way.

[Robert Collins (lifeless)]

I thought we had a dupe of this but I can't find it.

It would be good to hide irrelevant frames, though that definition gets tricky when you consider we develop testtools with testtools.

[Jonathan Lange (jml)]

Bug 660852 isn't a dupe, but it's close. I think we can hide those frames without causing too many problems for testtools own development.