public void Invoke_warns_on_error()
        {
            var reporter = new TestOperationReporter();

            var startup = new StartupInvoker(
                reporter,
                MockAssembly.Create(typeof(BadStartup)));

            var services = startup.ConfigureServices();

            Assert.NotNull(services);
            Assert.Equal(
                "warn: " + DesignStrings.InvokeStartupMethodFailed(
                    "ConfigureServices",
                    nameof(BadStartup),
                    "Something went wrong."),
                reporter.Messages[0]);
        }