Kotlin Testing

Tests prove observable contracts. Coverage measures exercised structure but does not prove migration completeness or behavioral equivalence.

Test design

Name the contract, source test, defect, risk, or incident each test protects.
Assert values, typed failures, ordering, state transitions, side effects, call counts, serialization bytes, cleanup, or externally observable timing boundaries.
Prefer real values and fakes at owned boundaries. Mock only costly or nondeterministic collaborators.
Use table/property tests for input partitions; retain each source case identity during migrations.
For coroutines, use virtual time and event-driven coordination. Never use unbounded waits or fixed sleeps as synchronization.
Reuse adapter conformance suites so every implementation receives the same contract assertions plus adapter-native tests.
Keep fixtures versioned and deterministic. Record seeds, locale, timezone, encoding, and platform assumptions.