Add fixture for asserting maximum number of database queries

[anrie]

Often I don't want to test against the exact number of queries performed by a particular piece of code but just be sure that changes to the codebase don't end up in an unnoticed excessive increase of queries.

django-test-plus has a really nice helper for this kind of scenario: https://github.com/revsys/django-test-plus#assertnumquerieslessthannumber---context

This PR tries to port the same functionality to pytest-django.

Open issues:

• No tests so far
• Does renaming assert_num_queries to assert_exact_num_queries make sense?

Cheers,
Andreas

[blueyed]

Please rebase, since our tests in master were failing with pytest 3.3.

[codecov-io]

Codecov Report

Merging #547 into master will increase coverage by 0.08%.
The diff coverage is 97.87%.

@@            Coverage Diff             @@
##           master     #547      +/-   ##
==========================================
+ Coverage   92.33%   92.42%   +0.08%     
==========================================
  Files          32       32              
  Lines        1710     1742      +32     
  Branches      142      143       +1     
==========================================
+ Hits         1579     1610      +31     
- Misses         94       95       +1     
  Partials       37       37

Flag	Coverage Δ
#dj110	84.67% <97.87%> (+0.22%)	⬆️
#dj111	86.73% <97.87%> (+0.18%)	⬆️
#dj18	85.47% <97.87%> (+0.33%)	⬆️
#dj19	84.55% <97.87%> (+0.23%)	⬆️
#dj20	84.95% <97.87%> (+0.22%)	⬆️
#dj21	84.95% <97.87%> (+0.22%)	⬆️
#mysql_innodb	84.95% <97.87%> (+0.22%)	⬆️
#mysql_myisam	84.9% <97.87%> (+0.22%)	⬆️
#postgres	88.28% <97.87%> (+0.16%)	⬆️
#py27	89.83% <97.87%> (+0.13%)	⬆️
#py34	84.55% <97.87%> (+0.23%)	⬆️
#py35	84.67% <97.87%> (+0.22%)	⬆️
#py36	85.41% <97.87%> (+0.21%)	⬆️
#sqlite	86.73% <97.87%> (+0.18%)	⬆️
#sqlite_file	84.55% <97.87%> (+0.23%)	⬆️

Impacted Files	Coverage Δ
pytest_django/plugin.py	86.04% <100%> (+0.04%)	⬆️
pytest_django/fixtures.py	97.05% <100%> (+0.14%)	⬆️
tests/test_fixtures.py	99.59% <96%> (-0.41%)	⬇️

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[anrie]

@blueyed I did a rebase and the tests are now passing.

[blueyed]

@lukaszb
What do you think?

[lukaszb]

I'd leave previous name - it might be less strict but it's how Django named their test method and I'm for consistency here.

Other than that I don't see anything wrong with max alternative.

[blueyed]

I agree with @lukaszb.

@anrie
Please change the existing fixture to keep the existing name.

[anrie]

@blueyed There you go!

[blueyed]

Rebased and fixed a warning reported by Sphinx.

[blueyed]

Extended it a bit to return the wrapped context manager, and added support for connection.
Does it look fine?

[anrie]

Looks very good to me!

[blueyed]

Thank you, merged!