Fiona Liao, a software engineer at Grafana Labs, encountered a bug in Prometheus while working on a Grafana Cloud project involving PromQL query generation. The bug, which led to double-counting of sample values during query evaluation, was discovered through integration tests designed to verify the correctness of generated queries. The issue stemmed from the memSafeIterator in Prometheus, which was not synchronizing correctly with its internal iterator, resulting in erroneous results. Specifically, the Seek() method updated only the internal iterator, causing the memSafeIterator to read incorrect sample values from the buffer. To resolve this, Liao added a Seek() method to the memSafeIterator, ensuring both iterators remained synchronized, and submitted the fix to Prometheus. This experience highlights the importance of integration tests in identifying and resolving software bugs, and Liao encourages interested individuals to consider opportunities at Grafana Labs, where similar challenging and rewarding work is undertaken.