MbUnit : TestDecoratorOverview

When you are tagging a method with ExpectedExceptionAttribute, you are actually "decorating it" with a wrapper that will intercept exceptions and check that they are of the right type.

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[Test]
[ExpectedException(typeof(ArgumentNullException))]
public void Test()
{
   throw new ArgumentNullException();
}

The ExceptedExceptionAttribute acts as a DynamicProxy around the Test invokation, doing some pre and post actions. Test decorators can also be applied directly to the fixture, in that case, they are applied to all the tests produced by the fixture. The example below shows how to make a fixture 'ignored':

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[TestFixture] 
[Ignore]
public class MyFixture
{
   ...
}

Implementation

All decorator inherit from the DecoratorPatternAttribute attribute and have to implement 1 method:

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public abstract IRunInvoker GetInvoker(IRunInvoker wrapper);

In this method, wrapper is the IRunInvoker instance that represents the method call. The GetInvoker is used to install additional funcitonalities. Therefore, implementing a custom decorator usually involves implementing a custom IRunInvoker. MbUnit also provides a base class for such IRunInvoker implementations: DecoratorRunInvoker.

Tutorial sample

This sample shows how a decorator can be used to change the current Culture and restore it afterwards. At first, we create a new CustomAttribute that inherits from DecoratorPatternAttribute. In the GetInvoker of this method, we return a IRunInvoker instance that does the job, ChangeCultureRunInvoker.

ChangeCultureRunInvoker.Execute is where the current culture is substituted and restored.

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using System;
using System.Collections;
using System.Threading; 
using System.Globalization;  

using MbUnit.Core.Invokers;
using MbUnit.Core.Framework;

namespace MbUnit.Demo
{
    [AttributeUsage(AttributeTargets.Method,AllowMultiple =false,Inherited = true)]
    public class ChangeCultureAttribute : DecoratorPatternAttribute
    {
        private string name;
        public ChangeCultureAttribute(string name)
        {
            if (name == null)
                throw new ArgumentNullException("null");
            this.name = name;
        }  

        public override IRunInvoker GetInvoker(IRunInvoker wrapped)
        {
             ChangeCultureRunInvoker invoker = 
               new ChangeCultureRunInvoker(this.name,wrapped);
            return invoker;
        } 

        internal class ChangeCultureRunInvoker : DecoratorRunInvoker
        {
           private string cultureName;
           public ChangeCultureRunInvoker(string cultureName, IRunInvoker invoker)
               :base(invoker)
           {
               this.cultureName = cultureName;
           }  

           public override Object Execute(
                object o, 
                IList args)
            {
                CultureInfo culture = null;  
                try
                {
                    culture = Thread.CurrentThread.CurrentCulture;
                    Thread.CurrentThread.CurrentCulture = new CultureInfo(cultureName);  
                    return this.Invoker.Execute(o, args);
                }
                finally
                {
                    if (culture!=null)
                        Thread.CurrentThread.CurrentCulture = culture;
                }
            }
        }
    }
}