test: Fix issue with flaky flagd RPC Resolver tests

[kylejuliandev]

This PR

Fix flaky tests but leveraging AutoResetEvent to callback at the point relevant for the test. Instead of always waiting for the flagdProviderEvent to be assigned, which happens before the cache purging, occassionally causing some tests to fail we use the reset event to wait before making the assertions.

Introduced in #515

Related Issues

Notes

Follow-up Tasks

How to test

[gemini-code-assist]

Summary of Changes

Hello @kylejuliandev, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly improves the stability of the "flagd" RPC Resolver tests. By introducing "AutoResetEvent" as a synchronization primitive, the tests now accurately wait for specific asynchronous events, such as "flagdProviderEvent" assignments or cache purges/deletions, to complete before making assertions. This change addresses intermittent failures by preventing race conditions and ensuring that test logic executes only when the system is in the expected state, leading to more reliable and consistent test results.

Highlights

• Enhanced Test Reliability: Implemented "AutoResetEvent" in "flagd" RPC Resolver tests to precisely synchronize test assertions with event callbacks and cache operations, eliminating flakiness caused by race conditions.
• Improved Synchronization: Replaced "Utils.AssertUntilAsync" with "AutoResetEvent.WaitOne" for more deterministic waiting, ensuring tests validate state only after critical asynchronous operations complete.

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[gemini-code-assist]

Code Review

This pull request effectively addresses the flaky tests by replacing a polling mechanism with AutoResetEvent for better synchronization in asynchronous test scenarios. The approach is sound and correctly implemented to make the tests more reliable. I have a couple of suggestions to further improve code quality by removing an unused variable and abstracting a magic number into a constant for better maintainability.