effect-testing-mocking

Testing & Mocking

When to use

• You need deterministic tests without external IO
• You want to inject mock services via layers

Mock Layer

const RepoTest = Layer.succeed(Repo, Repo.of({ find: () => Effect.succeed(mock) }))

Provide Test Impl

const result = yield* Effect.provide(program, RepoTest)

Test Clock

// Provide a deterministic Clock or use platform TestClock layer if available

Guidance

• Keep tests focused and fast; avoid network by mocking services
• Provide layers explicitly to match program requirements
• Keep tests close to real interfaces; do not reshape app code for tests
• Use .Default layers for quick wiring; add custom mock layers per test
• Favor small smoke tests that run quickly and fail fast

Pitfalls

• Leaking real IO into tests → flakiness
• Over-mocking internals → brittle tests; mock at service boundary

Cross-links

• Layers & Services for DI patterns
• Time/Logging for deterministic time and observable output

Local Source Reference

CRITICAL: Search local Effect source before implementing

The full Effect source code is available at docs/effect-source/. Always search the actual implementation before writing Effect code.

Key Source Files

• Layer: docs/effect-source/effect/src/Layer.ts
• TestClock: docs/effect-source/effect/src/TestClock.ts
• TestContext: docs/effect-source/effect/src/TestContext.ts

Example Searches

# Find Layer.succeed patterns for mocks
grep -F "Layer.succeed" docs/effect-source/effect/src/Layer.ts

# Study TestClock operations
grep -F "TestClock" docs/effect-source/effect/src/TestClock.ts

# Find test helpers
grep -F "TestContext" docs/effect-source/effect/src/TestContext.ts

# Look at Layer test examples
grep -F "Layer.succeed" docs/effect-source/effect/test/Layer.test.ts

Workflow

1. Identify the testing API you need (e.g., Layer.succeed, TestClock)
2. Search docs/effect-source/effect/src/Layer.ts for the implementation
3. Study the types and testing patterns
4. Look at test files for usage examples
5. Write your code based on real implementations