separate server binding to port from other app config

this seems a bit crude but allows running the tests and having them take
care of setting up the port to use

test/home.test.ts

@@ -1,5 +1,6 @@
 import * as supertest from "supertest";
-const request = supertest("http://localhost:3000");
+const app = require("../src/app");
+const request = supertest(app);
 
 describe("GET /", () => {
   it("should return 200 OK", () => {