Investigate using rspec-preconditions gem to perform fixture verification expectations

MR: Pending

Description

Follow up on this thread to investigate the possible use of https://github.com/on-site/rspec-preconditions or a similar home-grown approach in cases where we want to validate that fixtures are properly set up.

https://github.com/on-site/rspec-preconditions might help here though 🤷

I like this idea, since I think we would be able to then update the Cop to ignore expectations in a preconditions block.

Acceptance criteria

• Consider adding rspec-preconditions gem, or preferably building our own version from scratch to avoid a dependency
• If added, convert all existing "fixture sanity checks" to be in precondition blocks, and ensure these do not cause RuboCop errors around expectations in before blocks.
• If not added, consider just deleting all the fixture sanity check expectations.

Implementation plan

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[Provide a high-level plan for implementation of this issue, including relevant technical and/or design details.]