Question

Is there any special support when you come to test callbacks with NUnit? Or some kind of of “best practice” which is better than my solution below?

I just started writing some tests and methods, so I have still full control – however I think it might be annoying if there are better ways to test callbacks thoroughly, especially if complexity is increasing. So this is a simple example how I am testing right now:

The method to be tested uses a delegate, which calls a Callback function, for instance as soon as a new xml element is being discovered in a stream. For testing purpose I pass the NewElementCallback Method to the delegate and store the arguments content in some test classes properties when the function is called. These properties I use for assertion. (Of course they are being reset in the test setup)

[Test]
public void NewElement()
{
    String xmlString = @"<elem></elem>";

    this.xml.InputStream = new StringReader(xmlString);
    this.xml.NewElement += this.NewElementCallback;

    this.xml.Start();

    Assert.AreEqual("elem", this.elementName);
    Assert.AreEqual(0, this.elementDepth);
}

private void NewElementCallback(string elementName, int elementDepth)
{
    this.elementName = elementName;
    this.elementDepth = elementDepth;
}

Answer 1

You could avoid the need for private fields if you use a lambda expression, that’s how I usually do this.

[Test]
public void NewElement()
{
    String xmlString = @"<elem></elem>";
    string elementName;
    int elementDepth;

    this.xml.InputStream = new StringReader(xmlString);
    this.xml.NewElement += (name,depth) => { elementName = name; elementDepth = depth };

    this.xml.Start();

    Assert.AreEqual("elem", elementName);
    Assert.AreEqual(0, elementDepth);
}

it makes your tests more cohesive and having fields on any test class is always asking for disaster!