How to use the @nebular/theme.NbChatModule.forRoot function in @nebular/theme

import { ChatSizesComponent } from './chat-sizes.component';
import { ChatTestComponent } from './chat-test.component';

@NgModule({
  declarations: [
    ChatColorsComponent,
    ChatConversationShowcaseComponent,
    ChatDropComponent,
    ChatMessageTypesShowcaseComponent,
    ChatShowcaseComponent,
    ChatSizesComponent,
    ChatTestComponent,
  ],
  imports: [
    CommonModule,
    NbChatModule.forRoot(),
    NbCardModule,
    ChatRoutingModule ],
})
export class ChatModule {}

import { ChatSizesComponent } from './chat-sizes.component';
import { ChatTestComponent } from './chat-test.component';

@NgModule({
  declarations: [
    ChatColorsComponent,
    ChatConversationShowcaseComponent,
    ChatDropComponent,
    ChatMessageTypesShowcaseComponent,
    ChatShowcaseComponent,
    ChatSizesComponent,
    ChatTestComponent,
  ],
  imports: [
    CommonModule,
    NbChatModule.forRoot(),
    NbCardModule,
    ChatRoutingModule ],
})
export class ChatModule {}

beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [ NbChatModule.forRoot() ],
    });

    fixture = TestBed.createComponent(NbChatFormComponent);
    chatFormComponent = fixture.componentInstance;

    fixture.detectChanges();
  });

declarations: [AppComponent],
  imports: [
    BrowserModule,
    BrowserAnimationsModule,
    HttpClientModule,
    AppRoutingModule,

    ThemeModule.forRoot(),

    NbSidebarModule.forRoot(),
    NbMenuModule.forRoot(),
    NbDatepickerModule.forRoot(),
    NbDialogModule.forRoot(),
    NbWindowModule.forRoot(),
    NbToastrModule.forRoot(),
    NbChatModule.forRoot({
      messageGoogleMapKey: 'AIzaSyA_wNuCzia92MAmdLRzmqitRGvCF7wCZPY',
    }),
    CoreModule.forRoot(),
  ],
  bootstrap: [AppComponent],
  providers: [
    { provide: APP_BASE_HREF, useValue: '/' },
  ],
})
export class AppModule {
}