[New-bugs-announce] [issue37712] Exception frames from unittest.TestCase.fail dependent on nesting

[Matthew Roeschke]

New submission from Matthew Roeschke <mroeschke at housecanary.com>:

With this toy example:

import unittest

def this_fails():
    a = 1 + None

class TestExample(unittest.TestCase):

    def test_this(self):
        try:
            this_fails()
        except Exception:
            self.fail('Fail')

if __name__ == '__main__':
    unittest.run()

I get the last frame for each chained exception:

Traceback (most recent call last):
  File "/Users/me/test.py", line 10, in test_this
    this_fails()
TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/me/test.py", line 12, in test_this
    self.fail('Fail')
AssertionError: Fail

But if the toy example contained a nested call, e.g.

    def helper(self):
        try:
            this_fails()
        except Exception:
            self.fail('Fail')

    def test_this(self):
        self.helper() 

I get the last 2 frames for each chained exception:

Traceback (most recent call last):
  File "/Users/me/test.py", line 10, in helper
    this_fails()
  File "/Users/me/test.py", line 4, in this_fails
    a = 1 + None
TypeError: unsupported operand type(s) for +: 'int' and 'NoneType'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/me/test.py", line 15, in test_this
    self.helper()
  File "/Users/me/test.py", line 12, in helper
    self.fail('Fail')
AssertionError: Fail

Ideally, it would be great if the traceback went back to the root of the exception regardless.

----------
components: Library (Lib)
messages: 348708
nosy: Matthew Roeschke
priority: normal
severity: normal
status: open
title: Exception frames from unittest.TestCase.fail dependent on nesting
type: behavior
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37712>
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