How to test websockets (gateways) using unit tests

I wrote a simple server adding a todo using sockets.

// todos.gateway.ts
import {
    SubscribeMessage,
    WebSocketGateway,
    OnGatewayInit,
    WebSocketServer,
    OnGatewayConnection,
    OnGatewayDisconnect,
} from '@nestjs/websockets';
import { Logger } from '@nestjs/common';
import { Socket, Server } from 'socket.io';
import { Todos } from './todos.entity';
import { TodosService } from './todos.service';

@WebSocketGateway()
export class TodosGateway implements OnGatewayInit, OnGatewayConnection, OnGatewayDisconnect {
    constructor(private todosService: TodosService) {}

    @WebSocketServer() server: Server;

    private logger: Logger = new Logger('TodosGateway');

    @SubscribeMessage('listToDoToServer')
    async handleListToDos(client: Socket, payload: string, data: { room: string; id: number }) {
        client.join(data.room);
        this.logger.log(`Room id: ${data.id}, Client id: ${data.id}`);
        const listDoto = await this.todosService.getToDos();
        this.server.to(data.room).emit('listToDoToClient', listDoto);
    }

    @SubscribeMessage('leaveRoom')
    handleRoomLeave(client: Socket, payload: string, room: string) {
        client.leave(room);
        this.logger.log(`Client leave room: ${room}`);
    }

    afterInit(server: Server) {
        this.logger.log('Init');
    }

    handleDisconnect(client: Socket) {
        this.logger.log(`Client disconnected: ${client.id}`);
    }

    handleConnection(client: Socket, ...args: any[]) {
        this.logger.log(`Client connected: ${client.id}`);
    }
}


// todos.gateway.spec.ts
import { Test, TestingModule } from '@nestjs/testing';
import { TodosGateway } from './todos.gateway';

describe('TodosGateway', () => {
    let gateway: TodosGateway;

    beforeEach(async () => {
        const module: TestingModule = await Test.createTestingModule({
            providers: [TodosGateway],
        }).compile();

        gateway = module.get<TodosGateway>(TodosGateway);
    });

    it('should be defined', () => {
        expect(gateway).toBeDefined();
    });
});

How to test sockets? I understand that you need to create mock functions, and which one I don’t understand.

I could not find information on socket testing in the documentation. Also, those examples that I find through Google did not suit me.