Preferable way to make a unit test with synctest package

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Summary

The problem at hand is ensuring that a fire-and-forget goroutine, specifically a call to HitCallback, is executed exactly once in a unit test. Key considerations include the use of mock expectations and synchronization mechanisms to verify the behavior of asynchronous code.

Root Cause

The root cause of the complexity in testing this scenario lies in the asynchronous nature of the HitCallback call. Since it’s a fire-and-forget operation, the response is ignored, making it challenging to ensure it’s called exactly once without additional synchronization or mocking mechanisms.

Why This Happens in Real Systems

This issue arises in real systems due to the following reasons:

  • Asynchronous programming: Fire-and-forget callbacks are common in asynchronous programming, where the immediate response isn’t the focus.
  • Testing complexities: Ensuring that these callbacks are executed as expected adds complexity to unit tests.
  • Non-deterministic behavior: Without synchronization, the execution of asynchronous callbacks can lead to non-deterministic test outcomes.

Real-World Impact

The real-world impact includes:

  • Flaky tests: Tests may fail intermittently if they don’t correctly handle asynchronous operations.
  • Missed bugs: Failing to ensure that critical callbacks are executed can mask bugs, leading to issues in production.
  • Difficulty in debugging: Debugging asynchronous code can be more challenging without proper synchronization or logging.

Example or Code

// Using the synctest package for synchronization
synctest.Test(s.T(), func(t *testing.T) {
    s.httpRepo.EXPECT().HitCallback(mock.Anything).Return(models.MQResponse{Status: true}, nil).Once()
    // Code under test goes here
    synctest.Wait() // Waits for the expected call to happen
})

How Senior Engineers Fix It

Senior engineers typically address this by:

  • Using mocking libraries effectively to set clear expectations for asynchronous calls.
  • Implementing synchronization mechanisms (like channels or synctest.Wait()) to ensure tests wait for the expected behavior.
  • Writing deterministic tests that account for the asynchronous nature of the code under test.

Why Juniors Miss It

Junior engineers might miss this due to:

  • Lack of experience with asynchronous programming and testing.
  • Insufficient understanding of how mocking libraries and synchronization mechanisms work.
  • Overlooking the importance of ensuring asynchronous callbacks are executed as expected in tests.