Testing express NodeJS endpoints using supertest

I'm trying to set up a test environment to test my typescript express nodejs endpoints but I can't seem to get it to work. I've installed:

1. jest
2. ts-jest
3. jest-junit
4. supertest
5. @types/supertest
6. @types/jest

this is how spec file looks:

import * as request from 'supertest';
import seed from '../../modules/contract/seed'; //empty seed function
import app from '../../index'; // export default app which is an express()

beforeAll(seed);

describe('contractService', () => {
  it('getContracts ', async () => {
    const res = await request(app).get('/getContracts');
    console.log(res.body);
  });
  it('makeContract makes and returns a new contract', async () => {
    const res = await request(app)
      .post('/makeContract')
      .send({
        name: 'testContract',
        startDate: '2019-10-3',
        challenges: []
      });
    expect(res.statusCode).toEqual(200);
    expect(res.body.challenges).toEqual([]);
    expect(res.body.name).toEqual('testContract');
    expect(res.body.startDate).toContain('2019-10-3');
  });
});

I get an error at the request(app) saying

This expression is not callable. Type 'typeof supertest' has no call signatures

contractService.spec.ts(1, 1): Type originates at this import. A namespace-style import cannot be called or constructed, and will cause a failure at runtime. Consider using a default import or import require here instead.

I don't know what to do because if I use require instead of import, I get the next error

TypeError: Cannot read property 'address' of undefined

it('getContracts ', async () => {
     const res = await request(app)
       .get('/')
        ^
       .expect(200);
});

index.ts

import './config/environment';
import http, { Server } from 'http';
import express, { Express, Router } from 'express';
import bodyParser from 'body-parser';
import mongoose from 'mongoose';
import connect from './database/index';
import patientRouter from './services/patientService';
import challengeRouter from './services/challengeService';
import contractRouter from './services/contractService';

let app: Express;

const startServer = async () => {
  try {
    await connect();
    app = express();
    const routes = Router();
    app.use(bodyParser.json());
    app.use(routes);
    // app.get('/', (req: Request, res: Response) => res.sendStatus(200));
    routes.get('/', (req, res) => res.send('OK'));
    // use routers from services
    routes.use('/', patientRouter);
    routes.use('/', challengeRouter);
    routes.use('/', contractRouter);
    const httpServer: Server = http.createServer(app);
    httpServer.listen(process.env.PORT, async () => {
      console.log(`🚀 Server ready at http://localhost:${process.env.PORT}`);
    });
    const shutdown = async () => {
      await new Promise(resolve => httpServer.close(() => resolve()));
      await mongoose.disconnect();
      if (process.env.NODE_ENV === 'test') return;
      process.exit(0);
    };
    process.on('SIGTERM', shutdown);
    process.on('SIGINT', shutdown);
    process.on('SIGQUIT', shutdown);
  } catch (e) {
    console.log(e);
  }
};

startServer();

export default app;

Jest config:

module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'node',
  testMatch: ['<rootDir>/**/__tests__/**/*.spec.ts'],
  testPathIgnorePatterns: ['/node_modules/'],
  coverageDirectory: './test-reports',
  coveragePathIgnorePatterns: ['node_modules', 'src/database', 'src/test', 'src/types'],
  reporters: ['default', 'jest-junit'],
  globals: { 'ts-jest': { diagnostics: false } }
};