playwright-msw

playwright-msw

A Mock Service Worker API for Playwright.

Setup

The example below shows how playwright-msw can be be used to create custom test fixtures which allow API calls to be automatically mocked, while also exposing the msw fixture so that mocks may be overridden on a per test basis. For an up to date example, please refer to test.ts.

import { test as base, expect } from "@playwright/test";
import { rest } from "msw";
import type { MockServiceWorker } from "playwright-msw";
import { createServer } from "playwright-msw";

const handlers = [
  rest.get("/api/users", (_, response, context) =>
    response(
      context.delay(500),
      context.status(200),
      context.json([
        {
          id: "bcff5c0e-10b6-407b-94d1-90d741363885",
          firstName: "Rhydian",
          lastName: "Greig",
        },
        {
          id: "b44e89e4-3254-415e-b14a-441166616b20",
          firstName: "Alessandro",
          lastName: "Metcalfe",
        },
        {
          id: "6e369942-6b5d-4159-9b39-729646549183",
          firstName: "Erika",
          lastName: "Richards",
        },
      ])
    )
  ),
];

export const test = base.extend<{
  msw: MockServiceWorker;
  rest: typeof rest;
}>({
  msw: [
    async ({ page }, use, info): Promise<void> => {
      const server = await createServer({
        page,
        info,
        handlers,
        webServerPort: info.config.webServer.port,
        baseWorkerServerPort: 9000,
        url: "/api/**",
      });

      await server.listen();
      // Test has not started to execute
      await use(server);
      // Test has finished executing
      await server.close();
    },
    {
      /**
       * Scope this fixture on a per test basis to ensure that each test has a
       * fresh copy of MSW.
       */
      scope: "test",
      /**
       * By default, fixtures are lazy; they will not be initalised unless they're
       * used by the test. Setting `true` here means that the fixture will be auto-
       * initialised even if the test doesn't use it.
       */
      auto: true,
    },
  ],
  rest,
});

export { expect };

Usage

The example below shows playwright-msw can be used to automatically mock API calls, while still allowing them to be mocked on a per test basis. For an up to date example, please refer to demo.spec.ts.

import { expect, test } from "../test";

test.describe.parallel("A demo of playwright-msw's functionality", () => {
  test("should use the default handlers without requiring handlers to be specified on a per-test basis", async ({
    page,
  }) => {
    await page.goto("/");
    await expect(page.locator('text="Alessandro Metcalfe"')).toBeVisible();
  });

  test.only("should allow mocks to be overridden on a per test basis", async ({
    page,
    msw,
    rest,
  }) => {
    await msw.use(
      rest.get("/api/users", (_, response, context) =>
        response(context.delay(250), context.status(403))
      )
    );
    await page.goto("/");
    await expect(page.locator('text="Alessandro Metcalfe"')).toBeHidden();
    await expect(page.locator('text="Failed to load users"')).toBeVisible();
  });
});