Making assertNumQueries print the list of queries executed on failure

[Dominic Rodger]

Currently, when assertNumQueries fails, the output is perhaps less helpful than it might be:

Traceback (most recent call last):
  File "/home/dom/.virtualenvs/kanisa/src/kanisa/kanisa/tests/views/public.py", line 31, in test_kanisa_root_view
    [banner1.pk, banner2.pk, banner3.pk, banner5.pk, ])
  File "/home/dom/.virtualenvs/kanisa/src/kanisa/.tox/py27-1.5.X/local/lib/python2.7/site-packages/django/test/testcases.py", line 195, in __exit__
    executed, self.num
AssertionError: 5 queries executed, 99 expected

When an assertNumQueries check fails, the first thing I (and I'd guess everyone else too) want to know is what queries ran, so it'd be awesome if an assertNumQueries failure printed the list of queries. Charlie Denton has a blog post describing how he does this (​http://meshy.co.uk/posts/debugging-assertnumqueries-tests/), but I'd like to see this included in Django itself - since it seems generally helpful.

This was discussed on django-developers (​https://groups.google.com/forum/#!topic/django-developers/8aUL9d9yyzg).

[Dominic Rodger]

Pull request created - ​https://github.com/django/django/pull/2055.

I'm not sure what kind of testing this needs - I don't want tests to depend on the SQL generated, so for now I've just amended the test for this to check that "Captured queries were" is included in the assertion. That feels a bit limited, so better ideas welcome.

This is my first non-docs contribution to Django, so do let me know if there's anything else that needs doing to get this committed.

[Simon Charette]

Test is looking good and the full test suite passes on Py2-3 SQlite3. The added test also passes on PostgreSQL (Py2-3) and MySQL.

Will commit with the minor suggested changes applied.

[Simon Charette <charette.s@…>]

In 5cd6477fd6ea31eeb4d281e8e431b7a5fb8038a1:

Fixed #21462 -- Made assertNumQueries print executed queries on failure.