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Effect - Define layers, consume them and test code depending on them
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| import { Context, Effect, Layer, pipe } from 'effect'; | |
| // ---------------------------------------------- | |
| // define layer | |
| class Logger extends Context.Tag('Logger')< | |
| Logger, | |
| { | |
| readonly info: (message: string) => Effect.Effect<void>; | |
| readonly error: (message: string) => Effect.Effect<void>; | |
| } | |
| >() {} | |
| type LoggerLayer = (typeof Logger)['Service']; | |
| // ---------------------------------------------- | |
| // define dependency constrained implementations | |
| const ConsoleLoggerLive = Layer.succeed(Logger, { | |
| info: (message: string) => | |
| pipe( | |
| Effect.succeed(console.info(message)), | |
| Effect.withSpan('logger-console/info'), | |
| ), | |
| error: (message: string) => | |
| pipe( | |
| Effect.succeed(console.error(message)), | |
| Effect.withSpan('logger-console/error'), | |
| ), | |
| }); | |
| const PinoLoggerLive = Layer.succeed(Logger, { | |
| // define implementation for pino ... | |
| }); | |
| // ---------------------------------------------- | |
| // consume layer | |
| // const task: Effect.Effect<void, never, Logger> | |
| const task = pipe( | |
| Effect.gen(function* () { | |
| const { error } = yield* Logger; | |
| error('oh no!'); | |
| }), | |
| ); | |
| // Providing logger implementation to run task | |
| Effect.runSync(pipe(task, Effect.provide(ConsoleLoggerLive))); | |
| // ---------------------------------------------- | |
| // creating a layer for tests | |
| import { vi } from 'vitest'; | |
| type LoggerTestLayerInput = { | |
| info?: Effect.Effect<void>; | |
| error?: Effect.Effect<void>; | |
| }; | |
| const makeLoggerTestLayer = (input: LoggerTestLayerInput) => { | |
| const errorMock = vi.fn().mockReturnValue(input.error); | |
| const infoMock = vi.fn().mockReturnValue(input.info); | |
| const make: Partial<LoggerLayer> = { | |
| error: errorMock, | |
| info: infoMock, | |
| }; | |
| return { | |
| LoggerTestLayer: Layer.succeed(Logger, Logger.of(make as never)), | |
| errorMock, | |
| infoMock, | |
| }; | |
| }; | |
| // ---------------------------------------------- | |
| // Using the layer in a test | |
| import { expect, describe, it } from 'vitest'; | |
| describe("my effect task", () => { | |
| it('should call error function', () => { | |
| const { LoggerTestLayer, errorMock } = makeLoggerTestLayer({ | |
| error: Effect.void, | |
| }); | |
| Effect.runSync( | |
| pipe( | |
| task, // Effect.Effect<void, never, Logger> | |
| Effect.provide(LoggerTestLayer), | |
| ), | |
| ); | |
| expect(errorMock).toHaveBeenCalledTimes(1); | |
| expect(errorMock).toHaveBeenCalledWith('oh no!'); | |
| }); | |
| }) |
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