import {TranslateFakeLoader,TranslateLoader,TranslateModule,TranslateService } from '@ngx-translate/core';

TestBed.configureTestingModule({
      imports: [
        ...
        TranslateModule.forRoot({
          loader: {
            provide: TranslateLoader,
            useClass: TranslateFakeLoader
          }
        })
      ],
      ...
      providers: [
        TranslateService
      ]