Castle Class Proxy for unit tests

Question

Scratching my head how to do this.

Suppose I had a concrete class Foo with 2 virtual methods, Execute() and GetFile(). Execute() will call GetFile. I want to make sure that when it does, GetFile() will throw a couple of different exceptions that Foo is supposed to handle gracefully in a testable manner.

For my unit tests, I am envisioning instantiating a DynamicProxy<Foo> from castle project where I intercept the GetFile() to throw the exception, and then invoke the DynamicProxy object's Execute() method, and test the results, but I can't see how to do this.

Is this possible/ practical? If so, what would the creation of the dynamic proxy object look like?

Answer 1

You don't need to handcode your own proxy because most the mocking frameworks support your scenario.

Here is an example using Moq (Moq will create a dynamic proxy internally for you):

public class SomeException : Exception { }

public class Foo
{
    public virtual int Execute()
    {
        try
        {
            GetFiles();
        }
        catch (SomeException)
        {
            return 1;
        }
        return 0;
    }

    public virtual void GetFiles()
    {
        //...
    }
}

[Test]
public void FooTest()
{
    var fooUnderTest = new Mock<Foo>();
    fooUnderTest.CallBase = true;
    fooUnderTest.Setup(f => f.GetFiles()).Throws(new SomeException());
    var result = fooUnderTest.Object.Execute();
    Assert.AreEqual(1, result);
}

You just need to take care to set Callbase = true which will:

Invoke base class implementation if no expectation overrides the member (a.k.a. "Partial Mocks" in Rhino Mocks): default is false.