Question

I want that my application catches the exceptions and e-mail them when running in production, but when I am running my MSTest unit tests I want it to throw the exceptions, so I can debug. My current code always e-mails the exceptions. There is any way to know if the current process was invoked by the unit tests?

One way I can think is to test the Enviroment.CurrentDirectory and similar variables. There is a better one?

Answer 1

This is a classic use case for dependency injection or a service locator. Instead of hardwiring your application to send emails, have your application get a notification service from the service locator, and have it call that. In production, configure the service locator to return an email sending service; in the test environment, configure it to return a service that does nothing, or add the notification to a list, or whatever.

You don’t need to go for the full whack dependency injection here: a very simple service locator will suffice. Similarly, the injection of the test notification service can be done through test fixture code. Here’s a really simple example:

public static class ServiceLocator
{
  private static INotificationService _notificationService = new EmailNotificationService();

  public static INotificationService NotificationService
  {
    get { return _notificationService; }
  }

  // For test use only
  public static void SetNotificationService(INotificationService notificationService)
  {
    _notificationService = notificationService;
  }
}

(A real service locator would provide a more flexible interface, along the lines of IServiceContainer/IServiceProvider, so that you could mock out multiple different services; this is just to illustrate the idea.)

Then in your test code:

[SetUp]
public void Setup()
{
  ServiceLocator.NotificationService = new DiscardingService();
}

(Using NUnit terminology here for the method that gets run before each test — not sure what the MSTest equivalent is.)

An advantage of this is that you can now test that the right notifications are being sent: have your test notification service capture the notifications in a list, and you can make assertions about that list to verify that notifications are being sent and are correct.

Again, note that this is not a full explanation of DI or service locators, and my sample code is by no means the best way to do it.