ExampleSignalR/TestProject/WebAppFactoryFixture.cs

using ExampleSignalR.Test.Services;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc.Testing;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;

namespace ExampleSignalR.Test;

public class WebAppFactoryFixture : WebApplicationFactory<ExampleSignalR.Program>
{

	protected override void ConfigureWebHost(IWebHostBuilder builder)
	{
		builder.ConfigureServices(ConfigureServices);
	}

	private void ConfigureServices(IServiceCollection services)
	{
		services.RemoveAll(typeof(IMessageService));
		services.AddTransient<IMessageService, MessageServiceTest>();
	}
}