add test cases and documentation for functions

test/repositories/UnoptimizedInMemoryRepositoryTests.test.ts

@@ -225,6 +225,14 @@ describe("UnoptimizedInMemoryRepository", () => {
     });
   });
 
+  describe("subscribeToEtaChanges", () => {
+    test("notifies listener if the eta has changed")
+  });
+
+  describe("unsubscribeFromEtaChanges", () => {
+
+  });
+
   describe("getOrderedStopByRouteAndStopId", () => {
     test("gets an ordered stop by route ID and stop ID", async () => {
       const mockOrderedStops = generateMockOrderedStops();
@@ -711,4 +719,4 @@ describe("UnoptimizedInMemoryRepository", () => {
       expect(result).toEqual([]);
     });
   });
-});
+});