refactor(core): Simplify createDeferredPromise, and add tests (no-changelog) (#10811)

packages/workflow/test/DeferredPromise.test.ts

@@ -0,0 +1,22 @@
+import { createDeferredPromise } from '@/DeferredPromise';
+
+describe('DeferredPromise', () => {
+	it('should resolve the promise with the correct value', async () => {
+		let done = false;
+		const deferred = createDeferredPromise<string>();
+		void deferred.promise.finally(() => {
+			done = true;
+		});
+		expect(done).toBe(false);
+		deferred.resolve('test');
+		await expect(deferred.promise).resolves.toBe('test');
+		expect(done).toBe(true);
+	});
+
+	it('should reject the promise with the correct error', async () => {
+		const deferred = createDeferredPromise();
+		const error = new Error('test error');
+		deferred.reject(error);
+		await expect(deferred.promise).rejects.toThrow(error);
+	});
+});