A Testing Mail Server For Unit Testing Email Functionality

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MailSo you are coding along riding that TDD high when you reach the point at which your code needs to send an email. What do you do now?

You might consider writing something that looks like:

EmailMessage email = new EmailMessage();
email.FromAddress = new EmailAddress(from);
email.AddToAddress(new EmailAddress(to));
email.Subject = subject;
email.BodyText = message;

SmtpServer smtpServer = new SmtpServer(SmtpServer, Port);

But you, being a TDD god(des) know better and quickly refactor that into some sleek code that uses an EmailProvider. This ensures that your code is not tied to any specific email implementation and will make unit testing your code easier. Just swap out your concrete email provider for a unit test specific email provider. Now your code looks like:

EmailProvider.Instance().Send(to, from, subject, message);

But a nagging thought still pulls at the edge of your consciousness. “Shouldn’t I unit test my concrete email provider and actually make sure the email gets sent correctly?

I certainly think so. As for the semantic arguments around whether this really constitutes an Integration Test as opposed to a Unit Test, please don’t bore me with your hang-ups. Either way, it deserves a test and what better way to test it than using something like MbUnit or NUnit.

Wouldn’t it be nice to test your email code like so?

DotNetOpenMailProvider provider = new DotNetOpenMailProvider();
NameValueCollection configValue = new NameValueCollection();
configValue["smtpServer"] = "";
configValue["port"] = "8081";
provider.Initialize("providerTest", configValue);

TestSmtpServer receivingServer = new TestSmtpServer();
    receivingServer.Start("", 8081);
                "Subject to nothing", 
                "Mr. Watson. Come here. I need you.");

// So Did It Work?
Assert.AreEqual(1, receivingServer.Inbox.Count);
ReceivedEmailMessage received = receivingServer.Inbox[0];
Assert.AreEqual("phil@example.com", received.ToAddress.Email);

That there code starts up a mail server, sends an email to it, and then checks that the mail server received the email. It also quickly checks the to address.

This is a snippet of an actual unit test within the Subtext codebase.

A long while ago I discovered a wonderful .NET based freeware mail server written by Ivar Lumi. I decided to write a wrapper specifically for unit testing scenarios. I added the TestSmtpServer to a new project named Subtext.UnitTesting.Servers in the Subtext VS.NET solution.

The wrapper parses incoming SMTP messages and adds an ReceivedEmailMessage instance to the Inbox custom collection. This makes it easy to quickly examine the email messages sent via SMTP in your unit test.

As this is a very early draft, there are some key limitations. I have yet to implement multi-part messages and attachments in the object model. I also punted on dealing with multiple to addresses. However, the ReceivedEmailMessage class does have a RawSmtpMessage property you can examine. For now, it works very well for simple text based emails.

Over time, I hope to implement these more complicated testing features as the need arises. However, if you find this useful and would like to contribute, please do!

If you want to view the latest code, check out these instructions for downloading the latest Subtext code using Subversion.

Or you can simply download this one project here, though keep in mind that I will be updating this project, but not necessarily this link to the project.

Since the project is specifically for unit testing purpsose, I went ahead and embedded the unit tests for this server within the project itself using MbUnit references. However you can simply swap out the assemblies and references to use NUnit if that is your preference.

Found a typo or error? Suggest an edit! If accepted, your contribution is listed automatically here.



14 responses

  1. Avatar for Thomas Wagner
    Thomas Wagner May 31st, 2006

    Love it! Love it! Love it!
    - I've got a guy building Ruby/Watir scripts that test web email capabilities but this really is a nice idea - I almost like it better than mine.

  2. Avatar for Haacked
    Haacked May 31st, 2006

    I first used the Lumisoft mail server at SkillJam. But I hadn't fleshed out the technique as far as this. You can probably dig out the code and see that I did something similar.

  3. Avatar for Ron
    Ron May 31st, 2006

    nDumbster does something similiar:

  4. Avatar for Greg Young
    Greg Young May 31st, 2006

    I posted some comments here http://geekswithblogs.net/g... but I do not see the value in this .. The only time your unit test will fail that a mock would not is when you either have a problem with your test code or environment.

  5. Avatar for Haacked
    Haacked May 31st, 2006

    Good point, but there are some specific scenarios that a mock cannot test as well as having access to the underlying SMTP message.

  6. Avatar for Andrew Stopford's Weblog
    Andrew Stopford's Weblog May 31st, 2006

    Phil shows how he has approached testing email functionality, sample code with unit tests (MbUnit) included...

  7. Avatar for colinramsay.co.uk
    colinramsay.co.uk May 31st, 2006

    And by "properly", I mean check that it actually arrives. How about A Testing Mail Server For Unit Testing Email Functionality?...

  8. Avatar for Community Blogs
    Community Blogs December 13th, 2006

    Last night a unit test saved my life ( with apologies ) . Ok, maybe not my life, but the act of writing

  9. Avatar for Community Blogs
    Community Blogs June 19th, 2007

    Testing code written for the web is challenging. Especially code that makes use of the ASP.NET intrinsic

  10. Avatar for SuperJason
    SuperJason November 6th, 2007

    Thank you very much. This came in handy on an email system I'm working on.
    I tried the ndumbster project, but it's ancient, and it didn't work for me. It would lock up when receiving a message with the .NET 2.0 SMTP client.

  11. Avatar for Jack
    Jack January 17th, 2008

    I am using Lumisoft Mail Server. I am using it in ASP .Net,C#.
    I have problem in adding user domain. Can any one send me the code to add user and domain details.

  12. Avatar for Andrew Thompson
    Andrew Thompson January 23rd, 2010

    Dang, looks useful, but I can't open the archive :-\ (Unexpected end of archive)

  13. Avatar for Sam
    Sam August 12th, 2014

    I have been using mail4Net, which has a unit test client. Their website has more information about unit testing emails: www.mail4net.com

  14. Avatar for Sanjay
    Sanjay September 2nd, 2016

    love it!!! yes. It is all about integration test!!