add similar test cases for previous stop

test/resolvers/OrderedStopResolverTests.test.ts

@@ -167,15 +167,42 @@ describe("OrderedStopResolvers", () => {
     }
 
     it("returns the previous stop if it exists", async () => {
+      // Arrange
+      const orderedStops = await setUpOrderedStopsInRepository();
 
+      // Act
+      const response = await getResponseForPreviousStopQuery(orderedStops[1].stopId);
+
+      // Assert
+      assert(response.body.kind === "single");
+      expect(response.body.singleResult.errors).toBeUndefined();
+
+      const previousStop = (response.body.singleResult.data?.system as any).route.orderedStop.previousStop;
+      expect(previousStop.stopId).toEqual(orderedStops[0].stopId);
+      expect(previousStop.routeId).toEqual(orderedStops[0].routeId);
     });
 
     it("returns null if there is no previous stop in the repository", async () => {
+      const orderedStops = await setUpOrderedStopsInRepository();
+      orderedStops[1].previousStop = undefined;
+      await repository.addOrUpdateOrderedStop(orderedStops[1]);
 
+      const response = await getResponseForPreviousStopQuery(orderedStops[1].stopId);
+
+      assert(response.body.kind === "single");
+      const nonexistentPreviousStop = (response.body.singleResult.data?.system as any).route.orderedStop.previousStop;
+      expect(nonexistentPreviousStop).toBeNull();
     });
 
     it("returns null if the current stop no longer exists", async () => {
+      const orderedStops = await setUpOrderedStopsInRepository();
+      await repository.removeStopIfExists(orderedStops[0].stopId);
 
+      const response = await getResponseForPreviousStopQuery(orderedStops[1].stopId);
+
+      assert(response.body.kind === "single");
+      const nonexistentPreviousStop = (response.body.singleResult.data?.system as any).route.orderedStop.previousStop;
+      expect(nonexistentPreviousStop).toBeNull();
     });
   });