Basic structure of the project

- Added a model with in-memory database, and routes, controller and
middleware to enable making initial CRUD calls to endpoints;

- Added jest and an initial test.

tests/topicController.test.ts

@@ -0,0 +1,22 @@
+import { Request, Response } from 'express';
+import { getTopics } from '../src/controllers/topicController';
+import { topics } from '../src/models/topic';
+
+describe('Topic Controller', () => {
+  it('should return an empty array when no topics exist', () => {
+    // Create mock objects for Request, Response, and NextFunction
+    const req = {} as Request;
+    const res = {
+      json: jest.fn(),
+    } as unknown as Response;
+
+    // Ensure that our in-memory store is empty
+    topics.length = 0;
+
+    // Execute our controller function
+    getTopics(req, res, jest.fn());
+
+    // Expect that res.json was called with an empty array
+    expect(res.json).toHaveBeenCalledWith([]);
+  });
+});