[Synapse] Test Coverage Improvements

[chamons]

This is a tracking issue to cover the test improvements in Synapse.

The goal is to provide basic coverage for each exposed client, and one test for each API.

Admittingly, this is primarily "happy path" coverage, but given the limited previous coverage, it's a good start.

It also let's us flush out some basic service issues.

Punch List

• Refactor shared code and build infrastructure
  • [Synapse] Rework and extend unit tests #18010
• Stub out test files for each client
  • [Synapse] Rework and extend unit tests #18010
• AccessControl
• Artifacts
  • [Synapse] Rework and extend unit tests #18010
  • [synapse] Add more Artifacts tests #18114
• ManagedPrivateEndpoints
• Monitoring
  • Existing tests provided solid coverage
• Spark
• Walk through broken [Ignore]'ed tests and make sure service team has issues
  • Marked up in code with [Synapse] API issues found in writing tests #18079
• Walk thorough [Ignore]'ed tests due to automation and research if we can extend test template to include needed resources

[jsquire]

Given the age of this issue, closing this as stale. If tests are still failing, please file a new issue.