[Robust Testing] Move tests to tests/unit/context

[MichelleArk]

addresses: #9961

Problem

Our unit tests are currently in files that don’t match the modules they are testing and are in a flat directory structure.

Solution

Tackle three unit test files and move them:

• test_providers.py to tests/unit/context
• test_query_header.py to tests/unit/context
  • also moved QueryHeaderContext into its own context
• move test_context.py to tests/unit/context

also: lots of unittest.TestCase deprecation!

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.15%. Comparing base (668fe78) to head (27aec66).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9966      +/-   ##
==========================================
+ Coverage   80.53%   88.15%   +7.61%     
==========================================
  Files         180      181       +1     
  Lines       22578    22581       +3     
==========================================
+ Hits        18184    19907    +1723     
+ Misses       4394     2674    -1720     

Flag	Coverage Δ
integration	85.47% <100.00%> (+4.93%)	⬆️
unit	62.09% <100.00%> (?)

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[QMalcolm]

Thank you! 🙂