Add Jest for unit testing (incomplete)

src/lib/api.test.ts

@@ -0,0 +1,20 @@
+import { Axios } from 'axios';
+import MockAdapter from 'axios-mock-adapter';
+import { HeaptraderAPI } from './api';
+import { expect, jest, test } from '@jest/globals';
+
+let mock: MockAdapter;
+
+class HeaptraderAPITest extends HeaptraderAPI
+{
+    constructor()
+    {
+        super("");
+        mock = new MockAdapter(this._axios);
+    }
+}
+
+test('check uptime', async () => {
+    const api = new HeaptraderAPI();
+    await api.heartbeat();
+});

src/lib/api.ts

@@ -3,16 +3,16 @@ import { consola } from 'consola/browser';
 import type { Listing, User } from './models';
 import { CreateListingRequestSchema, LoginRequestSchema, RegisterRequestSchema, type CreateListingRequest, type LoginRequest, type RegisterRequest } from './requests';
 
-interface RequestError
+export interface RequestError
 {
     message: string;
 }
 
-class HeaptraderAPI
+export class HeaptraderAPI
 {
-    private _axios: Axios;
-    private _user?: User;
-    private _lastUserUpdateTimeMs?: number;
+    protected _axios: Axios;
+    protected _user?: User;
+    protected _lastUserUpdateTimeMs?: number;
 
     constructor(baseURL: string = "http://localhost")
     {