Journey to an FP Test Harness
summary
Case study traces converting Play API tests from Future-heavy, mutable traits into a pure-FP harness built with Cats IO and state transformers. Code moves from blocking Play helpers and cake-style self-types to a single TestOp type defined as StateT[IO], uses IndexedStateT to model phase changes, and maintains a cache of clients for multi-user tests. Play result helpers get rewritten, the harness composes and runs deterministically, and the experiment succeeds.
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chapters (10)
- 0:00Start
- 0:57Background
- 3:05Functional Tests
- 4:17Test Code Is Code
- 11:06Monads
- 15:18Api Tests
- 15:53Futures and Side-Effects
- 18:05Helper Methods
- 21:57Clean Up the Play Helpers
- 27:04Model Phase Changes in the Test
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