update yarn script commands

backend/package.json

@@ -5,9 +5,9 @@
   "scripts": {
     "prebuild": "tslint -c tslint.json -p tsconfig.json --fix",
     "build": "tsc",
-    "prestart": "npm run build",
+    "prestart": "yarn run build",
     "start": "node .",
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "jest"
   },
   "dependencies": {
     "dotenv": "^8.2.0",
@@ -18,7 +18,12 @@
     "@types/dotenv": "^8.2.0",
     "@types/express": "^4.17.2",
     "@types/express-validator": "^3.0.0",
+    "@types/jest": "^25.1.2",
     "@types/node": "^13.7.1",
+    "@types/supertest": "^2.0.8",
+    "jest": "^25.1.0",
+    "supertest": "^4.0.2",
+    "ts-jest": "^25.2.0",
     "tslint": "^6.0.0",
     "typescript": "^3.7.5"
   }