How to unit test a service which uses caching?

@mallory_cormier 

Unit testing a service that uses caching can be a bit tricky, as the presence of cache data can affect the outcome of your tests. However, there are several strategies you can use to effectively test a service that uses caching:

1. Mock the caching layer: One approach is to mock the caching layer in your tests so that you can control the data that is stored and retrieved during testing. This way, you can ensure that each test starts with a clean slate and that the cache is set up with known data for each test case.
2. Test cache hits and misses: Write test cases to verify that the service behaves correctly when data is found in the cache (cache hit) and when data is not found in the cache (cache miss). This will help you ensure that the service is interacting correctly with the caching layer.
3. Use time-based mocking: Another approach is to use time-based mocking to simulate the passage of time in your tests. This can help you verify that the service interacts correctly with the caching layer for scenarios where cached data expires or is evicted.
4. Use different cache configurations: Test your service with different cache configurations (e.g., different cache sizes, expiry times, eviction policies) to ensure that it behaves correctly under varying caching conditions.
5. Verify cache interactions: Finally, verify that the service interacts correctly with the caching layer by checking that data is stored, retrieved, and invalidated as expected. This can help you catch any bugs or issues with the caching logic in your service.

By following these strategies, you can effectively test a service that uses caching and ensure its reliability and correctness in different caching scenarios.