Merge commit '36c66dd290d3ce6eb1ccd310d0c658d4a32bb8eb' as 'repos/effect'

repos/effect/ai-docs/src/09_testing/20_layer-tests.ts

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+/**
+ * @title Testing services with shared layers
+ *
+ * How to test Effect services that depend on other services.
+ */
+import { assert, describe, it, layer } from "@effect/vitest"
+import { Array, Context, Effect, Layer, Ref } from "effect"
+
+export interface Todo {
+  readonly id: number
+  readonly title: string
+}
+
+// Create a test ref service that can be used to store and manipulate test data
+// in layers.
+export class TodoRepoTestRef extends Context.Service<TodoRepoTestRef, Ref.Ref<Array<Todo>>>()("app/TodoRepoTestRef") {
+  static readonly layer = Layer.effect(TodoRepoTestRef, Ref.make(Array.empty()))
+}
+
+class TodoRepo extends Context.Service<TodoRepo, {
+  create(title: string): Effect.Effect<Todo>
+  readonly list: Effect.Effect<ReadonlyArray<Todo>>
+}>()("app/TodoRepo") {
+  static readonly layerTest = Layer.effect(
+    TodoRepo,
+    Effect.gen(function*() {
+      const store = yield* TodoRepoTestRef
+
+      const create = Effect.fn("TodoRepo.create")(function*(title: string) {
+        const todos = yield* Ref.get(store)
+        const todo = { id: todos.length + 1, title }
+        yield* Ref.set(store, [...todos, todo])
+        return todo
+      })
+
+      const list = Ref.get(store)
+
+      return TodoRepo.of({
+        create,
+        list
+      })
+    })
+  ).pipe(
+    // Provide the test ref layer as a dependency for the test repo layer.
+    // Use Layer.provideMerge so the tests can also access the test ref directly
+    // if needed.
+    Layer.provideMerge(TodoRepoTestRef.layer)
+  )
+}
+
+class TodoService extends Context.Service<TodoService, {
+  addAndCount(title: string): Effect.Effect<number>
+  readonly titles: Effect.Effect<ReadonlyArray<string>>
+}>()("app/TodoService") {
+  static readonly layerNoDeps = Layer.effect(
+    TodoService,
+    Effect.gen(function*() {
+      const repo = yield* TodoRepo
+
+      const addAndCount = Effect.fn("TodoService.addAndCount")(function*(title: string) {
+        yield* repo.create(title)
+        const todos = yield* repo.list
+        return todos.length
+      })
+
+      const titles = repo.list.pipe(
+        Effect.map((todos) => todos.map((todo) => todo.title))
+      )
+
+      return TodoService.of({
+        addAndCount,
+        titles
+      })
+    })
+  )
+
+  // You would also add a live layer here that provides real dependencies for
+  // production code.
+  //
+  // static readonly layer = Layer.effect(TodoService, ...).pipe(
+  //   Layer.provide(TodoRepo.layer)
+  // )
+
+  static readonly layerTest = this.layerNoDeps.pipe(
+    // Provide the test repo layer as a dependency for the test service layer.
+    // Use `Layer.provideMerge` so the tests can also access the test repo
+    // directly if needed, as well as the test ref through the repo layer.
+    Layer.provideMerge(TodoRepo.layerTest)
+  )
+}
+
+// `layer(...)` creates one shared layer for the block and tears it down in
+// `afterAll`, so all tests inside can access the same service context.
+layer(TodoRepo.layerTest)("TodoRepo", (it) => {
+  it.effect("tests repository behavior", () =>
+    Effect.gen(function*() {
+      const repo = yield* TodoRepo
+      const before = (yield* repo.list).length
+      assert.strictEqual(before, 0)
+
+      yield* repo.create("Write docs")
+
+      const after = (yield* repo.list).length
+      assert.strictEqual(after, 1)
+    }))
+
+  it.effect("layer is shared", () =>
+    Effect.gen(function*() {
+      const repo = yield* TodoRepo
+      const before = (yield* repo.list).length
+      assert.strictEqual(before, 1)
+
+      yield* repo.create("Write docs again")
+
+      // because the layer is shared between tests, the todo created in the
+      // previous test is still present, so the count should be 2, not 1
+      const after = (yield* repo.list).length
+      assert.strictEqual(after, 2)
+    }))
+})
+
+describe("TodoService", () => {
+  it.effect("tests higher-level service logic", () =>
+    Effect.gen(function*() {
+      const ref = yield* TodoRepoTestRef
+      const service = yield* TodoService
+      const count = yield* service.addAndCount("Review docs")
+      const titles = yield* service.titles
+
+      assert.isTrue(count >= 1)
+      assert.isTrue(titles.some((title) => title.includes("Review docs")))
+
+      // You can also access the test ref directly to make assertions about the
+      // underlying data.
+      const todos = yield* Ref.get(ref)
+      assert.isTrue(todos.length >= 1)
+    }).pipe(Effect.provide(TodoService.layerTest)))
+})