How to get Python `unittest` `assertRaises` methods to print `msg` parameter? - python-unittest

Question

In the following, the test should fail and print the msg parameter. But it doesn't.
with self.assertRaises(ZeroDivisionError, msg="Unexpected denominator"):
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This parameter (msg) works in every other assert* method. It seems highly unlikely that something so fundamental could be broken in unittest, so what's the deal?
Here's a complete program that demonstrates the problem:
#!/usr/bin/env python2
import unittest
class TestAssertRaisesMsgParam(unittest.TestCase):
def test_assert_raises_msg(self):
"""
Test unittest `assertRaises` msg param is printed
"""
with self.assertRaises(ZeroDivisionError, msg="Unexpected denominator"):
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if __name__ == '__main__':
unittest.main()
Here's my interaction with it:
$ ls -l assertRaises.py
-rwxr-xr-x 1 tom users 440 Jun 10 14:04 assertRaises.py
$ python -m unittest assertRaises
F
======================================================================
FAIL: test_assert_raises_msg (assertRaises.TestAssertRaisesMsgParam)
----------------------------------------------------------------------
Traceback (most recent call last):
File "assertRaises.py", line 14, in test_assert_raises_msg
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AssertionError: ZeroDivisionError not raised
----------------------------------------------------------------------
Ran 1 test in 0.000s
FAILED (failures=1)
And some system info:
$ /usr/bin/env python2
Python 2.7.13 (default, Mar 22 2017, 12:31:17) [GCC] on linux2
$ uname -a
Linux ... 4.4.62-18.6-default #1 SMP Fri Apr 21 16:14:48 UTC 2017 (84f9824) x86_64 x86_64 x86_64 GNU/Linux

Answer 1

Your code works on my box:
$ python -m unittest tester
F
======================================================================
FAIL: test_assert_raises_msg (test.TestAssertRaisesMsgParam)
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\Users\danth\src\test.py", line 12, in test_assert_raises_msg
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AssertionError: ZeroDivisionError not raised : Unexpected denominator
----------------------------------------------------------------------
Ran 1 test in 0.001s
FAILED (failures=1)
Make sure you run your test like this:
python -m unittest name_of_test_file