pytest is leaking frames of tests that fail

[nicoddemus]

The test below reproduces the problem:

import weakref

class Obj:
    pass

ref = None

def test1():
    obj = Obj()
    global ref
    ref = weakref.ref(obj)
    assert 0

def test2():
    assert ref() is None

This fails with:

================================== FAILURES ===================================
____________________________________ test1 ____________________________________

    def test1():
        obj = Obj()
        global ref
        ref = weakref.ref(obj)
>       assert 0
E       assert 0

test_foo.py:15: AssertionError
____________________________________ test2 ____________________________________

    def test2():
>       assert ref() is None
E       assert <test_foo.Obj object at 0x0000017302911198> is None
E        +  where <test_foo.Obj object at 0x0000017302911198> = ref()

test_foo.py:19: AssertionError
========================== 2 failed in 0.04 seconds ===========================

The reference to test1's frame should not have leaked. If we comment the assert 0 line, then both tests pass.

xref: pytest-dev/pytest-qt#187