update query resolver tests to modify the context

test/resolvers/QueryResolverTests.test.ts

@@ -1,6 +1,10 @@
 import { describe, expect, it } from "@jest/globals";
 import { generateMockPassioSystems } from "../testHelpers/mockDataGenerators";
-import { setupTestServerContext, setupTestServerHolder } from "../testHelpers/apolloTestServerHelpers";
+import {
+  buildSystemForTesting,
+  setupTestServerContext,
+  setupTestServerHolder
+} from "../testHelpers/apolloTestServerHelpers";
 import assert = require("node:assert");
 import { addMockShuttleToRepository, addMockStopToRepository } from "../testHelpers/repositorySetupHelpers";
 import { ScheduledNotification } from "../../src/repositories/NotificationRepository";
@@ -50,6 +54,13 @@ describe("QueryResolvers", () => {
     `;
 
     it("returns a system for an ID from the repository", async () => {
+      context.systems = [
+        buildSystemForTesting(),
+        buildSystemForTesting(),
+      ];
+      context.findSystemById = (_: string) => context.systems[1];
+      context.systems[1].id = "test-id";
+
       const systems = context.systems;
       const systemToGet = systems[1];
 
@@ -69,6 +80,8 @@ describe("QueryResolvers", () => {
     });
 
     it("returns null if there is no system", async () => {
+      context.findSystemById = (_: string) => null;
+
       const response = await holder.testServer.executeOperation({
         query,
         variables: {