Refactor dependents tests using library usecase

[Jyuart]

Fixes #1571

Utilize library use cases for dependents tests and refactor them to make them more readable.

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[codecov-commenter]

Codecov Report

Merging #1572 (57135d5) into master (848a138) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1572   +/-   ##
=======================================
  Coverage   92.61%   92.61%           
=======================================
  Files         142      142           
  Lines        6353     6353           
=======================================
  Hits         5884     5884           
  Misses        469      469           

Flag	Coverage Δ
pytest-backend	92.61% <100.00%> (ø)

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

Impacted Files	Coverage Δ
db/dependents/dependents_utils.py	100.00% <100.00%> (ø)

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[silentninja]

We should add a self-referential field to the dataset instead of creating it in the test case. I have added an issue for it here mathesar-foundation/mathesar-data-playground#5.

Don't worry about it making the change now, just add a to-do, so that we can refactor it later.

[silentninja]

Test cases are throwing up an error because it is not able to determine the schema, instead of using a raw SQL statement, a better option would be to replace with an equivalent function db.columns.operations.create.create_column

[silentninja]

Looks good to me, Thanks for the PR @Jyuart!