Update Legacy Class-based tests to Pytest

[data-sync-user]

A significant portion of our testing (integration, load, etc) utilize a mix of class-based tests and modern fixtures. This makes modifying and updating the tests difficult, as there are two competing architecture patterns. Additionally, class-based tests are less reliable when invoking modern test fixtures in Pytest. This could also be slowing down our tests or resulting in unexpected results.

The goal is to update our class-based test logic to use discrete, individualized test functions with reusable test fixtures, all under the Pytest framework paradigm.

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