Question

public class MyBaseClass
{
    protected void OnSomeEvent(EventContext context)
    {
         SomeType  = _someService.DoSomeLogic(context);
    }

    public SomeType SomeType { get; private set; } 
}

MyBaseClass works some magic to initialise a public property value when an event is triggerd in the process pipline.

public class MyClass : MyBaseClass
{
    public string Foo()
    {
        if (SomeType.SomeLogic())
            throw new InvalidOpertaionException();

        return "huzzah";
    }
}

The flow in other classes depends on SomeType being initialised.

How can I unit test MyClass.Foo()?

[TestMethod]
public void Foo_ReturnsHuzzah()
{
    var result = new MyClass().Foo(); 
    Assert.IsHuzzah(result);   
}

Answer 1

This type of temporal coupling (the event must be raised before the call to Foo is valid) is often considered a design flaw so the first thing I would do is revisit the design to make sure what I have is right.

If you don’t want to go that route, the easiest solution is to initialize SomeType with a Null Object implementation of SomeType like so…

class NullSomeType : SomeType
{
    public override bool SomeLogic() { return false; }
}

Then you default SomeType with the Null Object in the constructor.

public MyBaseClass()
{
   SomeType = new NullSomeType();
}