add NotificationService method and test case stub

src/services/NotificationService.ts

@@ -250,4 +250,12 @@ export class NotificationService {
     }
     return this.deviceIdsToDeliverTo[tuple.toString()].has(deviceId);
   }
+
+  /**
+   * Return all scheduled notification for the given device ID.
+   * @param deviceId
+   */
+  public async getAllScheduledNotificationsForDevice(deviceId: string): Promise<ScheduledNotificationData[]> {
+    return [];
+  }
 }

test/services/NotificationServiceTests.test.ts

@@ -230,4 +230,14 @@ describe("NotificationService", () => {
       expect(http2.connect as jest.Mock).toHaveBeenCalledTimes(0);
     });
   });
+
+  describe("getAllScheduledNotificationsForDevice", () => {
+    it("returns scheduled notifications for the device ID", async () => {
+
+    });
+
+    it("returns an empty array if there are no notifications", async () => {
+
+    });
+  });
 });