Use ruff linting; F811 will prevent duplicate test function names

[jonathan-s]

Here we use linting to check that we don't get any duplicate function names in tests. Specifically F811 covers this.

We get some other linting for free, and have the possibility to expand on linting rules if we want.

So in that sense, perhaps using coverage for python test_*.py becomes redundant?

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 98.53%. Comparing base (d549fbe) to head (59e8c1c).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
tests/filters/test_addslashes.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #56      +/-   ##
==========================================
- Coverage   98.53%   98.53%   -0.01%     
==========================================
  Files          29       29              
  Lines        4909     4908       -1     
  Branches     1621     1621              
==========================================
- Hits         4837     4836       -1     
  Misses         62       62              
  Partials       10       10              

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[LilyFirefly]

Overall I like this, but there's a few questions I have.

I'd still prefer to keep measuring coverage for tests though - it provides that extra guarantee that the test code is actually being run as expected.

[jonathan-s]

I'd still prefer to keep measuring coverage for tests though

Fair enough, though there will likely be some false positives (ie coverage saying that we get reduced coverage) for some time if we go with using xfail. Which I think is a useful placeholder for tests that need fixing once they are possible.

[LilyFirefly]

I missed it when reviewing before, but I think the reason ruff is complaining is because django_template and rust_template are unused.

Both test_addslashes01 and test_addslashes02 refer to a self.engine, but this doesn't exist because these aren't methods on a unittest test class.

[jonathan-s]

See #57