Move all tests under root test dir

[katybaulch]

Description

As the test helper functions are used by both the integration tests and the unit tests, move all tests under a 'tests' directory in the project root and move the helpers out of the unit test directory into this top level 'tests' folder.

Fix all linting errors as well.

Proposed version

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Type of change

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• Bug fix
• New feature
• Breaking change

How Has This Been Tested?

Ran tests locally

Reviewer Checklist

• The PR represents a single feature (small drive-by fixes are also ok)
• The PR includes tests that are sufficient for the level of risk
• The code is sufficiently commented, particularly in hard-to-understand areas
• Any required documentation updates have been made
• Any TODOs added are captured in future tickets
• No FIXMEs remain

[diversemix]

Looking good 😎