How to do e2e test in nestjs using mock data

I have an api in controller of nestjs.
First it checks wheter there is a center info or no.
After that, it makes a client.

  public async createClient(
    @Body() createClientDto: CreateClientDto,
    @Req() req,
    @Res() res,
  ) {
    const { centerId } = createClientDto;

    let center = null;
    try {
      center = await this.centersReadService.findCenter(centerId);
    } catch (err) {
      throw new HttpException(
          errorLog: err.message,
    if (!center) {
      throw new HttpException(
           popup: 'There is no center"
    await this.clientCreateService.createClient(createClientDto)
    return res.json({})

I made e2e test about this api.
It runs on 'docker-compose', so this app-test is running on localhost:20000.
I hope that it dosen't run new app with new port.
In this test, I want to get 'center=null' by findCenter method regardless of 'centerId' of 'createClientDto'.
Is is possible that some methods return fixed value using e2e test?

import { INestApplication } from '@nestjs/common';
import * as request from 'supertest';
import { t_CreateClientDto } from './mock-data';

describe('Masters Clients Post (e2e)', () => {
  let app: INestApplication;
  const testUrl = 'http://localhost:20000';

  it('can't create a client since there is no center.', () => {
    return request(testUrl)
      .expect('Content-Type', /json/)
      .expect((res) => {
        expect(res.body.popup).toBe('There is no center');