mocktime

Mocktime is a term used in software development to describe techniques and tools that simulate or control the progression of time within a program. By decoupling code from the actual system clock, mocktime enables deterministic testing of time-dependent logic, such as expirations, timeouts, retries, and scheduled tasks.

Implementation generally provides a replaceable time source, often via dependency injection or monkeypatching, so production code reads time from a clock interface while tests substitute a mock clock. This can involve freezing time at a fixed instant, advancing time in controlled steps, or simulating long-running intervals without real waiting.

Applications span unit and integration tests, simulations, and event-driven systems where timing behavior is critical. Examples include validating token lifetimes, cache TTLs, backoff strategies, cron-like schedulers, and feature flags that depend on the current date or time of day.

Advantages include deterministic tests, faster execution, and easier reproduction of edge cases. Disadvantages include the risk of masking real-world timing bugs and accidental coupling to the mock environment; careful isolation and a path to revert to real time are recommended.

Related concepts include time mocking, fake timers, virtual time, and time travel testing.