From cd2852fdcc58c4459da8b9cc9d5c80747e5cca81 Mon Sep 17 00:00:00 2001
From: Liam DeBeasi <liamdebeasi@users.noreply.github.com>
Date: Fri, 8 Apr 2022 12:12:32 -0400
Subject: [PATCH] test(playwright): add event spies (#25080)

---
 core/src/utils/test/playwright/eventSpy.ts    | 100 ++++++++++++++++++
 .../{playwright.ts => playwright/fixtures.ts} |  28 ++++-
 core/src/utils/test/playwright/index.ts       |   2 +
 3 files changed, 129 insertions(+), 1 deletion(-)
 create mode 100644 core/src/utils/test/playwright/eventSpy.ts
 rename core/src/utils/test/{playwright.ts => playwright/fixtures.ts} (84%)
 create mode 100644 core/src/utils/test/playwright/index.ts

diff --git a/core/src/utils/test/playwright/eventSpy.ts b/core/src/utils/test/playwright/eventSpy.ts
new file mode 100644
index 0000000000..6e10808cf1
--- /dev/null
+++ b/core/src/utils/test/playwright/eventSpy.ts
@@ -0,0 +1,100 @@
+import type { IonicPage } from './fixtures';
+
+/**
+ * The EventSpy class allows
+ * developers to listen for
+ * a particular event emission and
+ * pass/fail the test based on whether
+ * or not the event was emitted.
+ * Based off https://github.com/ionic-team/stencil/blob/16b8ea4dabb22024872a38bc58ba1dcf1c7cc25b/src/testing/puppeteer/puppeteer-events.ts#L64
+ */
+export class EventSpy {
+  /**
+   * Keeping track of a cursor
+   * ensures that no two spy.next()
+   * calls point to the same event.
+   */
+  private cursor = 0;
+  private queuedHandler: (() => void)[] = [];
+  public events: Event[] = [];
+
+  constructor(public eventName: string) {}
+
+  get length() {
+    return this.events.length;
+  }
+
+  public next() {
+    const { cursor } = this;
+    this.cursor++;
+
+    const next = this.events[cursor];
+    if (next) {
+      return Promise.resolve(next);
+    } else {
+      /**
+       * If the event has not already been
+       * emitted, then add it to the queuedHandler.
+       * When the event is emitted, the push
+       * method is called which results in the
+       * Promise below being resolved.
+       */
+      let resolve: () => void;
+      const promise = new Promise<void>((r) => (resolve = r));
+      // @ts-ignore
+      this.queuedHandler.push(resolve);
+
+      return promise.then(() => this.events[cursor]);
+    }
+  }
+
+  public push(ev: Event) {
+    this.events.push(ev);
+    const next = this.queuedHandler.shift();
+    if (next) {
+      next();
+    }
+  }
+}
+
+/**
+ * Initializes information required to
+ * spy on events.
+ * The ionicOnEvent function is called in the
+ * context of the current page. This lets us
+ * respond to an event listener created within
+ * the page itself.
+ */
+export const initPageEvents = async (page: IonicPage) => {
+  page._e2eEventsIds = 0;
+  page._e2eEvents = new Map();
+
+  await page.exposeFunction('ionicOnEvent', (id: number, ev: any) => {
+    const context = page._e2eEvents.get(id);
+    if (context) {
+      context.callback(ev);
+    }
+  });
+};
+
+/**
+ * Adds a new event listener in the current
+ * page context to updates the _e2eEvents map
+ * when an event is fired.
+ */
+export const addE2EListener = async (page: IonicPage, eventName: string, callback: (ev: any) => void) => {
+  const id = page._e2eEventsIds++;
+  page._e2eEvents.set(id, {
+    eventName,
+    callback,
+  });
+
+  await page.evaluate(
+    ([eventName, id]) => {
+      window.addEventListener(eventName as string, (ev: Event) => {
+        (window as any).ionicOnEvent(id, ev);
+      });
+    },
+    [eventName, id]
+  );
+};
diff --git a/core/src/utils/test/playwright.ts b/core/src/utils/test/playwright/fixtures.ts
similarity index 84%
rename from core/src/utils/test/playwright.ts
rename to core/src/utils/test/playwright/fixtures.ts
index f8bec9e6ac..8af41e90b0 100644
--- a/core/src/utils/test/playwright.ts
+++ b/core/src/utils/test/playwright/fixtures.ts
@@ -9,10 +9,15 @@ import type {
 } from '@playwright/test';
 import { test as base } from '@playwright/test';
 
-type IonicPage = Page & {
+import { EventSpy, initPageEvents, addE2EListener } from './eventSpy';
+
+export type IonicPage = Page & {
   goto: (url: string) => Promise<null | Response>;
   setIonViewport: () => Promise<void>;
   getSnapshotSettings: () => string;
+  spyOnEvent: (eventName: string) => Promise<EventSpy>;
+  _e2eEventsIds: number;
+  _e2eEvents: Map<number, any>;
 };
 
 type CustomTestArgs = PlaywrightTestArgs &
@@ -124,6 +129,27 @@ export const test = base.extend<CustomFixtures>({
       });
     };
 
+    /**
+     * Creates a new EventSpy and listens
+     * on the window for an event.
+     * The test will timeout if the event
+     * never fires.
+     *
+     * Usage:
+     * const ionChange = await page.spyOnEvent('ionChange');
+     * ...
+     * await ionChange.next();
+     */
+    page.spyOnEvent = async (eventName: string): Promise<EventSpy> => {
+      const spy = new EventSpy(eventName);
+
+      await addE2EListener(page, eventName, (ev: Event) => spy.push(ev));
+
+      return spy;
+    };
+
+    initPageEvents(page);
+
     await use(page);
   },
 });
diff --git a/core/src/utils/test/playwright/index.ts b/core/src/utils/test/playwright/index.ts
new file mode 100644
index 0000000000..90dcacbd8b
--- /dev/null
+++ b/core/src/utils/test/playwright/index.ts
@@ -0,0 +1,2 @@
+export * from './fixtures';
+export * from './eventSpy';