public void OperationStart_CorrectEventContent()
        {
            var source     = new DiagnosticListener("Autofac");
            var subscriber = new MockSubscriber();

            subscriber.Enable(DiagnosticEventKeys.OperationStart);
            source.Subscribe(subscriber, subscriber.IsEnabled);

            var operation = MockResolveOperation();
            var request   = MockResolveRequest();

            source.OperationStart(operation, request);
            var e = Assert.Single(subscriber.Events);

            Assert.Equal(DiagnosticEventKeys.OperationStart, e.Key);
            Assert.IsType <OperationStartDiagnosticData>(e.Value);
        }