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

• Identify the testing API you need (e.g., Layer.succeed, TestClock)

• Search docs/effect-source/effect/src/Layer.ts for the implementation

• Study the types and testing patterns

• Look at test files for usage examples

• Write your code based on real implementations

Real source code > documentation > assumptions

Real-world snippet: Build a comprehensive Test layer

export const TestLayer = (input?: TestLiveInput) => Effect.gen(function* () { const tempDir = tempy.temporaryDirectory({ prefix: 'test' }) const cwd = (yield* setupFixtureFolder({ fixture: input?.fixture, tempDir })) ?? tempDir

const NodeOsTest = Layer.succeed(NodeOs, new NodeOs({ homedir: cwd, arch: 'arm64', platform: 'darwin' }))
const NodeProcessTest = Layer.succeed(NodeProcess, new NodeProcess({ cwd, platform: 'darwin', arch: 'arm64' }))

const ToolkitsRepoTest = Layer.succeed(ComposioToolkitsRepository, new ComposioToolkitsRepository({
  getToolkits: () => Effect.succeed([]),
  getToolsAsEnums: () => Effect.succeed([])
}))

const layers = Layer.mergeAll(
  Console.setConsole(yield* MockConsole.effect),
  CliConfig.layer(ComposioCliConfig),
  NodeProcessTest,
  Layer.provideMerge(ComposioUserContextLive, Layer.merge(BunFileSystem.layer, NodeOsTest)),
  ToolkitsRepoTest,
  EnvLangDetector.Default,
  JsPackageManagerDetector.Default,
  BunFileSystem.layer,
  BunContext.layer,
  MockTerminal.layer,
  BunPath.layer
)

return layers

}).pipe( Logger.withMinimumLogLevel(LogLevel.Debug), Effect.scoped, Layer.unwrapEffect, Layer.provide(Layer.setConfigProvider(input?.baseConfigProvider ?? ConfigProvider.fromMap(new Map([])))) )

References

• Agent Skills overview: https://www.anthropic.com/news/skills

• Skills guide: https://docs.claude.com/en/docs/claude-code/skills