Added waitFor method in PubSub

src/main/PubSub.ts

@@ -32,6 +32,23 @@ export class PubSub<T = void> {
     }
   }
 
+  /**
+   * Waits for a message that satisfies the given predicate to be published and resolves with that message.
+   *
+   * @param predicate A function that takes the message as a parameter and returns true if the message satisfies the condition, otherwise false.
+   * @returns A promise that resolves with the published message that satisfies the predicate.
+   */
+  waitFor(predicate: (message: T) => boolean): Promise<T> {
+    return new Promise(resolve => {
+      const unsubscribe = this.subscribe(message => {
+        if (predicate(message)) {
+          resolve(message);
+          unsubscribe();
+        }
+      });
+    });
+  }
+
   /**
    * Adds a listener that would receive all messages published via {@link publish}.
    *

src/test/PubSub.test.ts

@@ -1,4 +1,4 @@
-import { PubSub } from '../main';
+import { PubSub, delay } from '../main';
 
 describe('PubSub', () => {
   test('publishes a message', () => {
@@ -54,4 +54,42 @@ describe('PubSub', () => {
     expect(listenerMock1).toHaveBeenCalledTimes(0);
     expect(listenerMock2).toHaveBeenCalledTimes(1);
   });
+
+  test('waits for a specific message and resolves with that message', () => {
+    const pubSub = new PubSub<number>();
+
+    pubSub
+      .waitFor(message => message === 42)
+      .then(message => {
+        expect(message).toBe(42);
+      });
+
+    pubSub.publish(10);
+    pubSub.publish(20);
+    pubSub.publish(42);
+    pubSub.publish(30);
+  });
+
+  test('does not resolve if no message matches the predicate', () => {
+    const listenerMock = jest.fn();
+    const pubSub = new PubSub<number>();
+
+    let result: number;
+
+    pubSub
+      .waitFor(message => message === 42)
+      .then(message => {
+        result = message;
+        listenerMock();
+      });
+
+    pubSub.publish(10);
+    pubSub.publish(20);
+    pubSub.publish(30);
+
+    delay(100).then(() => {
+      expect(result).toBeUndefined();
+      expect(listenerMock).toHaveBeenCalledTimes(0);
+    });
+  });
 });