Allows you to check sent E-mails in your .NET project component tests without installing SMTP on your test machine. Server stub is .NET Standard 2.0 library.

Just install Nuget package using Package Manager Console in VS

Install-Package SmtpServerStub -Version 1.1.0

Or using NuGet Package Manager, search for SmtpServerStub package.

Firs of all you will need to initialize and start SmtpServerStub server. The simplest way to do this is to write following code in one time setup in a base test. Which will run once in the begining of your test run. By default stub will start on 25 port of localhost.

[OneTimeSetUp]
public void RunBeforeAllTest()
{
    var settings = new SmtpServerSettings();
    Server = new SmtpServer(settings);
    Server.Start();
    Console.WriteLine("Server Started");
}

To make your tests more independent you may need to reset server stub state before each test. Do this by adding "before each" method to base test. Reseting server state is required to cleare list of already received E-mails, drop all assigned to server instance event listeners and finish all asynchronous tasks, which can be created for receiving other messages.

[SetUp]
public void RunBeforeAnyTest()
{
    Server.ResetState();
    Console.WriteLine("Server has been reset");
}

Aftet tests have finished running you may need to gracefully stop SMTP server stub.

[OneTimeTearDown]
public void RunAfterAllTestsFinished()
{
    Server.Stop();
    Console.WriteLine("Server Stopped");
}

In your inherited from base tests you will be able to perform following checks:

[Test]
public void ContainsCorrectEmailSubject()
{
    CallYourServiceToSendMail();

    var receivedMail = Server.GetReceivedMails()[0];
    receivedMail.Subject.Should().Be("Subject of email");
}

GetReceivedMails() method will wait till all started mail receives are finished and will return List of mail objects. Which contain main data you wish to check.

Server stub should be initialized with instance of SmtpServerStub.Dtos.SmtpServerSettings class or instance of class which implements ISmtpServerSettings interface. It contains following parameters:

• IpAddress is instance of IPAddress and serves to specifies IpAddress to which SMTP server should bind.
• Port is usual integer number and specifies port which stub should listen for incoming e-mails.
• Certificate is instance of X509Certificate2 and should be specified if you have enabled SSL in your e-mail sending functions. This certificate should be valid on you test machine. As SMTP server stub will use it to authenticate as server when it will be requested by client.
  As second parameter SmtpServer constructor may also receive implementation of SmtpServerStub.Dtos.ILogger which can be usefull while debuging of your tests and seeing why stub has faild message reception. Overall initialization can look in following way:

class SomeLogger : ILogger
{
    public void LogInfo(string message)
    {
        Console.WriteLine(message);
    }

    public void LogError(string message)
    {
        Console.WriteLine(message);
    }

    public void LogWarning(string message)
    {
        Console.WriteLine(message);
    }
}

And in base test one time setup:

var logger = new SomeLogger();
var settings = new SmtpServerSettings
    {
        IpAddress = IPAddress.Any,
        Port = 4637,
        Certificate = new X509Certificate2("certificate/file/path", "certificate*passrord", X509KeyStorageFlags.MachineKeySet)
    };
Server = new SmtpServer(settings, logger);
Server.Start();
Console.WriteLine("Server Started");

When call of your component method just starts send mail procedure but there is no guaranty that by the time method returned control to test thread sending has finished you may need to have possibility to know when message has fully received by SMTP server stub. For this case server implements event OnEmailReceived. As firs argument of this event listener instance of received server will be passed as second argument instance of SmtpServerStub.Dtos.EmailReceivedEventArgs class will appear. This object will contain received e-mail.

Server.OnEmailReceived += (sender, args) =>
{
    receivedMessages.Add(args.MailMessage);
};

Definitely this approach of testing may require much more magic with ManualResetEvent-s wait-ers and timeouts to stabilize your tests. Also such tests may run longer than synchronous tests, depending on how your application manages asynchronous operartions and priorities mail sending tasks. Some examples as variant how it can be done you can see in asyncronous integration tests of this project

Synchronous check exapmples
Asynchronous check exapmples
Simplified tests without required SSL encryption

• AppVeyor - Continuous Integration solution for Windows

• NUnit
• NSubstitute
• Fluent Assertions

• Valentin Kostiuk - GitHub Page

This project is licensed under the MIT License - see the LICENSE file for details