playwright-intercept 🎭

This fixture extension provides a Cypress-influenced API (like cy.intercept) for mocking and intercepting network requests in Playwright.

Features

Mock and intercept GET, POST, PUT, PATCH and DELETE responses
Craft dynamic responses at runtime using data from request params & bodies
Assert that requests were made to a specific URL
Assert the content of request bodies
Wait for a request to be made before continuing
Support for named route params (eg. /api/:apiVersion/callback/:id)
Strongly typed in TypeScript
Test coverage

Installation (npm)

npm i playwright-intercept --save-dev

Setup

Simply extend your base test fixture with the Intercept class, providing optional global configuration options:

fixturePathPrefix is the path to your mock data folder, eg. a folder of JSON files containing default response bodies
To avoid Playwright log spam, staticExtensions are extensions of files that should never be intercepted

import * as base from "@playwright/test";
import { Intercept } from "playwright-intercept";

const test = base.extend<BaseFixtures>({
  intercept: async ({ page }, use) => {
    await use(
      new Intercept(page, {
        fixturePathPrefix: path.join(process.cwd(), "tests"),
        staticExtensions: ['js', 'css', 'png', 'jpg', 'svg'],
      })
    );
  },
});

Basic Usage

test("Can submit form", async ({ page, intercept }) => {
  // first, set up the intercept, for example:
  const apiFormCallback = intercept.post({
    url: "/api/form/:id",
    statusCode: 200,
    body: {
      status: "success",
    },
    // you can also pass a file for the response body:
    // fixture: "path/to/response-body.json",
    //
    // and modify it on the fly:
    // modifier: ({ body, params }) => {
    //   if (params.id === "foo") {
    //     body.status = "bar";
    //   }
    //   return body;
    // },
    //
    // or pass a handler function for more advanced use cases:
    // handler: ({ route, request, params }) => {
    //   // `route` and `request` are both normal Playwright objects
    //   return route.fulfill({
    //     status: 200,
    //     contentType: 'application/json',
    //     body: `That named route param was ${params.id}`,
    //   });
    // },
  });

  await page.goto("/my-form");

  await page.fill('input[name="name"]', "Bar");

  await page.locator("#submit-button").click();

  await apiFormCallback.wait();

  await expect(apiFormCallback.requests[0].postDataJSON()).toBe({
    name: "Bar",
  });

  apiFormCallback.update({
    statusCode: 400,
    body: {
      status: "fail",
    }
  });

  await page.locator("#submit-button").click();

  await apiFormCallback.wait();

  await page.waitForSelector('div[role="alert"]');
});

Tip

This repo's tests folder contains examples that demonstrate the setup and functionality of playwright-intercept.

Suggested Implementation Pattern

We recommend you create fixtures of Intercept instances, logically grouped together. To see this pattern demonstrated, check out collection-of-intercepts-as-fixture.spec.ts in this repo.

We understand that everybody has their own preferred implementation pattern, so if you've found another great way to structure your Intercept instances in your Playwright codebase, please let us know in a PR or Issue!

API

`intercept[.get, .post, .patch, .put, .delete]`

type BaseOptions = {
  url: string;
  statusCode?: number;
};

type MimeTypeOption = {
  mimeType?: string;
};

type ModifierOption = {
  modifier?: (args: {
    body: any;
    params: Record<string, string>;
    request: Request;
  }) => any;
};

type BodyOption = {
  body: Buffer | object | string;
};

type FixtureOption = {
  fixture:
    | string
    | ((args: { route: Route; params: Record<string, string> }) => string);
};

type HandlerOption = {
  handler: (args: {
    route: Route;
    params: Record<string, string>;
    request: Request;
  }) => void;
};

export type InterceptOptions = BaseOptions &
  (
    | (MimeTypeOption & ModifierOption & (BodyOption | FixtureOption))
    | HandlerOption
    | { statusCode: number }
  );

At test runtime, InterceptSurface provides some methods and reactive attributes to help you assert requests.

`.wait({ timeout?: number })`

Resolves promise if a request has been made to the URL via selected method.

await myIntercept.wait({ timeout: 1000 });

`.requests`

Gives you direct access to all requests made to the URL.

expect(myIntercept.requests[0].postData()).toEqual({
  body: "foo"
});

expect(myIntercept.requests).toHaveLength(2);

`.update(InterceptOptions | (InterceptOptions) => InterceptOptions)`

Allows you to change the options of an intercept post-initialization for the lifetime of the test spec.

myIntercept.update({
  statusCode: 400,
  body: { id: 1 },
});

Contributing

Contributions are welcome! Please open an issue or PR if you have any suggestions or improvements.

alectrocute/playwright-intercept