Allow listening for page requests in tests (#34204)

test/lib/browsers/base.ts

@@ -1,3 +1,5 @@
+export type Event = 'request'
+
 // This is the base Browser interface all browser
 // classes should build off of, it is the bare
 // methods we aim to support across tests
@@ -68,6 +70,8 @@ export class BrowserInterface {
   deleteCookies(): BrowserInterface {
     return this
   }
+  on(event: Event, cb: (...args: any[]) => void) {}
+  off(event: Event, cb: (...args: any[]) => void) {}
   async loadPage(url: string, { disableCache: boolean }): Promise<any> {}
   async get(url: string): Promise<void> {}
 

test/lib/browsers/playwright.ts

@@ -1,4 +1,4 @@
-import { BrowserInterface } from './base'
+import { BrowserInterface, Event } from './base'
 import fs from 'fs-extra'
 import {
   chromium,
@@ -28,6 +28,23 @@ export async function quit() {
 
 class Playwright extends BrowserInterface {
   private activeTrace?: string
+  private eventCallbacks: Record<Event, Set<(...args: any[]) => void>> = {
+    request: new Set(),
+  }
+
+  on(event: Event, cb: (...args: any[]) => void) {
+    if (!this.eventCallbacks[event]) {
+      throw new Error(
+        `Invalid event passed to browser.on, received ${event}. Valid events are ${Object.keys(
+          event
+        )}`
+      )
+    }
+    this.eventCallbacks[event]?.add(cb)
+  }
+  off(event: Event, cb: (...args: any[]) => void) {
+    this.eventCallbacks[event]?.delete(cb)
+  }
 
   async setup(browserName: string) {
     if (browser) return
@@ -84,6 +101,9 @@ class Playwright extends BrowserInterface {
     page.on('pageerror', (error) => {
       console.error('page error', error)
     })
+    page.on('request', (req) => {
+      this.eventCallbacks.request.forEach((cb) => cb(req))
+    })
 
     if (opts?.disableCache) {
       // TODO: this doesn't seem to work (dev tools does not check the box as expected)