Question

I have defined two events with custom event arguments and associated raising methods. Now I wonder what and how the event should be tested. How should I analyze the code to find candidates for unit testing?

Answer 1

The way I test events is as follows:

Suppose this is your object:

public class MyEventRaiser
{
    public event EventHandler<string> MyEvent = delegate { };

    public void Process(string data)
    {
        // do something interestuing

        Thread.Sleep(2000);

        if (!string.IsNullOrEmpty(data))
        {
            this.MyEvent(this, data + " at: " + DateTime.Now.ToString());
        }
    }
}

Therefore your Subject Under Test is: MyEventRaiser and you want to test the method Process. You need to test that the event is raised when certain conditions are met, otherwise, the event should not be raised.

To do it, I use this framework (that I use always in my tests) FluentAssertions, this framewrok can be used with any test engine like MSTest, NUnit, MSpec, XUnit, etc

The tests look like:

[TestClass]
public class CustomEventsTests
{
    [TestMethod]
    public void my_event_should_be_raised()
    {
        var sut = new MyEventRaiser();

        sut.MonitorEvents();

        sut.Process("Hello");

        sut.ShouldRaise("MyEvent").WithSender(sut);
    }

    [TestMethod]
    public void my_event_should_not_be_raised()
    {
        var sut = new MyEventRaiser();

        sut.MonitorEvents();

        sut.Process(null);

        sut.ShouldNotRaise("MyEvent");
    }
}

You need to use the following namespaces:

using FluentAssertions;
using FluentAssertions.EventMonitoring;