// The TestStartup class provides all globally registered services for our tests.
public class TestStartup : Startup
{
        public TestStartup(IConfiguration configuration)
            : base(configuration)
        {
        }

        public void ConfigureTestServices(IServiceCollection services)
        {
            // Register all web application services.
            base.ConfigureServices(services);

            // Replace all custom services which need mocks.
            services.ReplaceTransient<IDateTimeProvider>(_ => DateTimeProviderMock.Create);
        }
}