Refactor event tests

[johannaengland]

Scope and purpose

Dependent on #1504. After I added tests to this file in that pull request I decided it is time to make this test easier to read and for new tests to be added if wanted.

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• Added a changelog fragment for towncrier
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.86%. Comparing base (423246f) to head (5952abf).
⚠️ Report is 22 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1961      +/-   ##
==========================================
+ Coverage   88.63%   88.86%   +0.23%     
==========================================
  Files         149      152       +3     
  Lines        7186     7283      +97     
==========================================
+ Hits         6369     6472     +103     
+ Misses        817      811       -6     

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[lunkwill42]

Overall a good restructure, though a couple of small things appear to need fixing...

Also, there is some setUp() logic that seems duplicated between classes. In lack of pytest fixtures (sigh), perhaps some of these could/should be factored out to a mixin class (I don't consider this a blocker for the PR, though, it's just a style hint)

[lunkwill42]

This appears to be a sibling of test_when_posting_close_event_for_stateless_incident_then_incident_does_not_change(), but makes no mention of _for_stateless_incident in its name..

[johannaengland]

Yes, because it's been moved to the class EventAPIStatelessIncidentTests, so we have the stateless in the class name already

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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