Mocking a layer in the Effect Typescript library involves creating a test layer that provides a m...

import { expect, describe, layer, beforeEach, vi } from "@effect/vitest"
...
describe("Surrealdb", () => {
  const mockSurreal = {
    select: vi.fn(),
    query: vi.fn(),
    close: vi.fn()
  }


  // Create a test layer with mocked database
  const TestDbLayer = Layer.scoped(
      DatabaseService,
      Effect.acquireRelease(
        Effect.sync(() => mockSurreal),
        (db) => Effect.promise(() => db.close())
      )as unknown as Effect.Effect<DatabaseService, never, Scope.Scope>
    )

  beforeEach(() => {
    vi.resetAllMocks()
    mockSurreal.close.mockResolvedValue(undefined)
  })
  layer(Surrealdb.Default)((it) => {
    it.effect("getItem - should retrieve item by id", () =>
      Effect.gen(function* () {
        mockSurreal.select.mockResolvedValue({ id: "user:123", name: "John" })
        const surrealdb = yield* Surrealdb.pipe(Effect.provide(TestDbLayer))
        const result = yield* surrealdb.getItem("user", "123")

        expect(mockSurreal.select).toHaveBeenCalledWith(new RecordId("user", "123"))
        expect(result).toEqual({ id: "user:123", name: "John" })
      }))

    it.effect("getItem - should handle database error", () =>
      Effect.gen(function* () {
        const error = new Error("DB failure")
        mockSurreal.select.mockRejectedValue(error)
        const result = yield* Effect.exit(Surrealdb.pipe(
          Effect.flatMap((s) => s.getItem("user", "123"))
        ))

        expect(result).toEqual(Exit.fail(
          new SurrealDbError("Couldn't retrieve item user:123", { cause: error })
        ))
      }))