How to Unit Test Events

Dave Kehring — Mon, 06 Oct 2008 15:35:17 GMT

If you have a class that contains an event, you'll want to write a unit test to test that the event gets fired at the right time and under the right conditions. The problem is that you would typically hook up an event handler in your unit test class that can run an assert to check if the event gets fired:

private bool _fired;
[Test] public void CheckVisiblityEvent()
{ _fired = false;
ImageGroupListItemViewModel vm = ImageGroupListItemViewModelFactory.Build();
vm.VisibilityChanged += new ImageGroupListItemViewModel.ImageGroupVisibilityChangedEventHandler(vm_VisibilityChanged);



vm.Visible = true; Assert.IsTrue(_fired);
} void vm_VisibilityChanged(object sender,
ImageGroupVisibilityEventArgs args) { _fired = true;
}

This is a bit sloppy. Instead, we could improve on this by using and anonymous method:

[Test] public void CheckVisiblityEvent()
{ bool fired = false;
ImageGroupListItemViewModel vm = ImageGroupListItemViewModelFactory.Build();
vm.VisibilityChanged += delegate(object sender,
ImageGroupVisibilityEventArgs e) { fired = true;
}; vm.IsVisible = true;
Assert.IsTrue(fired); }

More compact and easier to follow. Plus, the test code is all in one place. We can improve this even more with a lambda expression:

[Test] public void CheckVisiblityEvent()
{ bool fired = false;
ImageGroupListItemViewModel vm = ImageGroupListItemViewModelFactory.Build();
vm.VisibilityChanged += (s, e) => fired = true;
vm.IsVisible = true;
Assert.IsTrue(fired); }

Error "The calling thread must be STA, because many UI components require this" in NUnit for WPF apps

Dave Kehring — Tue, 12 Aug 2008 13:52:59 GMT

While trying to create unit tests for view models (using the Model-View-ViewModel pattern), I came across a problem while trying to execute unit tests from NUnit. The error I recevied was:

The calling thread must be STA, because many UI components require this.

A quick search on Google yielded an answer.

However, the configuration file in the post was incorrect and was noted by a commentor. For expediency, I have included the correct configuration text below:

< configSections>
   <sectionGroup name="NUnit">
      <section type="System.Configuration.NameValueSectionHandler" name="TestRunner"></section>
   </sectionGroup>
</configSections>>

< NUnit>
   <TestRunner>
      <add value="STA" key="ApartmentState"></add>
   </TestRunner>
</NUnit>>

Dave Kehring - Unit Testing

How to Unit Test Events

Error "The calling thread must be STA, because many UI components require this" in NUnit for WPF apps