Compare unit tests for edge cases

[chilagrow]

Description

Closes #1616.

Readiness checklist

• I added tests for new functionality or bugfixes.
• I ran task all, and it passed.
• I added/updated comments for both exported and unexported top-level declarations (functions, types, etc).
• I checked comments rendering with task godocs.
• I ensured that the title is good enough for the changelog.
• (for maintainers only) I set Reviewers (@FerretDB/core), Assignee, Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

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Name	Status	Preview	Updated
ferret-db	✅ Ready (Inspect)	Visit Preview	Dec 6, 2022 at 9:13AM (UTC)

[codecov]

Codecov Report

Merging #1624 (7e0a588) into main (8521c1e) will decrease coverage by 0.23%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1624      +/-   ##
==========================================
- Coverage   68.18%   67.95%   -0.24%     
==========================================
  Files         285      285              
  Lines       13766    13766              
==========================================
- Hits         9387     9355      -32     
- Misses       3443     3466      +23     
- Partials      936      945       +9     

Impacted Files	Coverage Δ
internal/handlers/pg/msg_create.go	77.21% <0.00%> (-6.33%)	⬇️
internal/util/version/version.go	70.58% <0.00%> (-4.42%)	⬇️
integration/setup/common.go	91.36% <0.00%> (-2.88%)	⬇️
internal/clientconn/conn.go	44.02% <0.00%> (-2.63%)	⬇️
internal/clientconn/listener.go	80.64% <0.00%> (-2.42%)	⬇️
internal/handlers/pg/pgdb/collections.go	52.27% <0.00%> (-2.28%)	⬇️
integration/setup/setup_compat.go	83.21% <0.00%> (-2.19%)	⬇️
internal/handlers/pg/pgdb/settings.go	44.21% <0.00%> (-2.05%)	⬇️
integration/setup/setup.go	85.47% <0.00%> (-1.71%)	⬇️
internal/handlers/common/filter.go	84.68% <0.00%> (-0.28%)	⬇️
... and 1 more

Flag	Coverage Δ
integration	63.92% <ø> (-0.24%)	⬇️
mongodb	?
pg	52.87% <ø> (-0.17%)	⬇️
tigris	37.28% <ø> (-0.03%)	⬇️
unit	26.82% <ø> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[AlekSi]

Let's add some test that is not skipped to ensure that it works

[rumyantseva]

I'm glad we have more clarity with these test cases! 👍