fix(gofeatureflag): fix unreachable code when flag not found

[thomaspoignant]

Description

This PR fixes issue #1618 where there was unreachable code in the EvaluationService class. The code to throw a FlagNotFoundError when a flag is not found was unreachable because it came after an early return statement.

Changes

• Moved the FLAG_NOT_FOUND check before the general error handling in EvaluationService.getEvaluation()
• This makes the FlagNotFoundError exception reachable when a flag is not found
• Added comprehensive unit tests to validate the fix

Testing

• Added unit tests that verify:
  • FlagNotFoundError is thrown when flag is not found
  • Other error codes still return error responses (regression test)
  • Successful evaluations continue to work correctly

All tests pass successfully.

Fixes #1618

[gemini-code-assist]

Summary of Changes

Hello @thomaspoignant, 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 resolves a critical bug in the go-feature-flag provider where the FlagNotFoundError was never thrown, leading to incorrect error reporting. The core change involves reordering the error handling logic within the EvaluationService to ensure that the specific flag not found error is correctly identified and propagated. This enhancement improves the robustness and accuracy of error handling in the feature flag evaluation process.

Highlights

• Unreachable Code Fix: Corrected an issue in the EvaluationService where the FlagNotFoundError was unreachable due to an early return statement.
• Error Handling Reordering: The check for FLAG_NOT_FOUND has been moved to occur before general error handling, ensuring that the specific FlagNotFoundError is thrown when a flag is not found.
• Comprehensive Unit Tests: New unit tests have been added to validate the fix, cover other error codes, and confirm that successful evaluations continue to work as expected.

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[gemini-code-assist]

Code Review

This pull request correctly fixes an unreachable code issue where a FlagNotFoundError would never be thrown. The logic is now corrected to check for FLAG_NOT_FOUND before handling other generic errors. The addition of comprehensive unit tests is excellent, as they validate the fix and cover regression and success cases. I've provided one suggestion to refactor the error handling logic for improved readability and maintainability.