Completando las pruebas del servicio HTTP

  describe('PUT', () => {
    it('should execute PUT', () => {

      service.put('/testing', {}).subscribe(res => {
        expect(res).toBeTruthy();
      });

      const req = httpMock.expectOne(environment.apiEndpoint + '/testing')
      expect(req.request.method).toBe('PUT');
    });
  });

  describe('DELETE', () => {
    it('should execute DELETE', () => {

      service.delete('/testing', {}).subscribe(res => {
        expect(res).toBeTruthy();
      });

      const req = httpMock.expectOne(environment.apiEndpoint + '/testing')
      expect(req.request.method).toBe('DELETE');
    });
  });```

Resolvi el error que tenia de la clase pasada. Estaba asignado mal al httpMock

import { TestBed, getTestBed } from '@angular/core/testing';
import { HttpClientTestingModule, HttpTestingController } from '@angular/common/http/testing';
import { ApiService } from './api.service';
import { environment } from 'src/environments/environment';
import { HttpHeaders } from '@angular/common/http';

fdescribe('ApiService', () => {
  let service: ApiService;
  let injector: TestBed;
  let httpMock: HttpTestingController;

  beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [ApiService],
      imports: [HttpClientTestingModule],
    });
  });

  beforeEach(() => {
    injector= getTestBed();
    service = TestBed.get(ApiService);
    httpMock = injector.get(HttpTestingController);
  });

  afterAll( () => {
    injector = null;
    service = null;
    httpMock = null;
  })
  it('Should be created', () =>{
    expect(service).toBeTruthy();
  })

  describe('GET', () => {

    it('Should execute GET', () => {
      const result = 'testing';
      service.get('/test').subscribe( response => {
        expect(response).toBe(result);
      })

      const req = httpMock.expectOne(environment.apiEndpoint + '/test');
      expect(req.request.method).toBe('GET')
      req.flush(result)
      
    })

    it('Should execute GET with headers', () => {
      const result = 'testing';
      const headers = new HttpHeaders().set('platzi-headers','cristian-rules')

      service.get('/test', headers).subscribe( response => {
        expect(response).toBe(result);
      })

      const req = httpMock.expectOne(environment.apiEndpoint + '/test');
      expect(req.request.headers.get('platzi-headers')).toBe('cristian-rules');
      expect(req.request.method).toBe('GET')
      req.flush(result)
      
    })

  })
  describe('POST', () => {
    it('should execute POST', () => {

      service.post('/testing', {}).subscribe(res => {
        expect(res).toBeTruthy();
      });

      const req = httpMock.expectOne(environment.apiEndpoint + '/testing')
      expect(req.request.method).toBe('POST');
    });
  });
  describe('PUT', () => {
    it('should execute PUT', () => {

      service.put('/testing', {}).subscribe(res => {
        expect(res).toBeTruthy();
      });

      const req = httpMock.expectOne(environment.apiEndpoint + '/testing')
      expect(req.request.method).toBe('PUT');
    });
  });

  describe('DELETE', () => {
    it('should execute DELETE', () => {

      service.delete('/testing', {}).subscribe(res => {
        expect(res).toBeTruthy();
      });

      const req = httpMock.expectOne(environment.apiEndpoint + '/testing')
      
      expect(req.request.method).toBe('DELETE');
    });
  });
});

  fdescribe('PUT', () => {
    fit('should excute a PUT petition', () => {
      const result = 'testing';
      service.put('/test', {}).subscribe((resp) => {
        expect(resp).toBeTruthy();
      });
      const req = httpMock.expectOne(`${environment.apiEndpoint}/test`);
      expect(req.request.method).toBe('PUT');
      expect(req.request.body).toEqual({});
      req.flush(result);
    });
  });

  fdescribe('DELETE', () => {
    fit('should excute a DELETE petition', () => {
      const result = 'testing';
      service.delete('/test').subscribe((resp) => {
        expect(resp).toBeTruthy();
      });
      const req = httpMock.expectOne(`${environment.apiEndpoint}/test`);
      expect(req.request.method).toBe('DELETE');
      req.flush(result);
    });
  });```