tests2.cs

public class Tests
{
    private WebApplicationFactory<Program> factory;

    [SetUp]
    public void Setup()
    {
        this.factory = new WebApplicationFactory<Program>().WithWebHostBuilder(builder =>
        {
            builder.ConfigureTestServices(services =>
            {
                services.AddScoped<IEmailService, FakeEmailService>();
            });
        });
    }
...