Conformance checking is a problem at MongoDB that involves ensuring the implementation of distributed algorithms conforms to their formal specifications. The company uses TLA+ (Temporal Logic and Applied), a formal specification language, to describe its algorithms. However, testing conformance has been challenging due to the complexity of the systems and the need for continuous synchronization between the spec and implementation. Two techniques used for conformance checking are trace-checking and test-case generation. Trace-checking involves generating execution traces from an implementation and verifying they conform to a specification, while test-case generation starts with a specification and checks its behaviors in the implementation. The authors of a 2020 paper experimented with these techniques on two MongoDB products but found that conformance checking was difficult due to the complexity of the systems and the need for continuous synchronization between the spec and implementation. However, they learned three lessons: it's hard to snapshot a multithreaded program's state, the implementation must conform to the specification, and test-case generation should extend easily to multiple specs. Since then, there has been progress in conformance checking techniques, including new tools and research prototypes that aim to make conformance checking more practical and accessible.