add NotificationService method and test case stub

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 () => {
+
+    });
+  });
 });