So i was trying to create an instance of a page class that inherits from some vendor code and has a bunch of dependencies in the constructor. Normally i would apply the pattern out of Michael Feather's book called Parameterize Constructor (basically add the dependency as a parameter and then mock it).

However, this was vendor code so i have no choice really and i really wasn't feeling interested in making a whole new chain of inheritance and implementation of interfaces just to seperate the dependencies so i started digging...

anyhow, the gist of it all was that i had a private static member that i wanted to put a value into, but it's on a sealed class and it's private and static so i can't override it and i can't inherit from it.

After reading a little more up on reflection (and examining HttpRuntime in the reflector to figure out the member names) i eventually got something like this put together:

                        [SetUp]

                        public void Setup()

                        {

                                    HttpRuntime theRuntimeInstance = GetTheRuntimeInstance();

                                    SetHttpRuntimePath(theRuntimeInstance, @"c:\dev\ProjectFolder\");

                        }

                        private static HttpRuntime GetTheRuntimeInstance()

                        {

                                    Type HttpRuntimeType = typeof (HttpRuntime);

                                    BindingFlags bindFlags = BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.Static;

                                    return HttpRuntimeType.InvokeMember(

                                                "_theRuntime", bindFlags,

                                                null, null, null

                                                ) as HttpRuntime;

                        }

                        private static void SetHttpRuntimePath(HttpRuntime theRuntimeInstance, string absolutePath)

                        {

                                    Type HttpRuntimeType = typeof (HttpRuntime);

                                    BindingFlags bindFlags = BindingFlags.NonPublic | BindingFlags.SetField | BindingFlags.Instance;

                                    HttpRuntimeType.InvokeMember("_appDomainAppPath", bindFlags

                                                                 , null, theRuntimeInstance, new object[] {absolutePath});

                                    HttpRuntimeType.InvokeMember("_appDomainAppVPath", bindFlags

                                                                 , null, theRuntimeInstance, new object[] {absolutePath});

                        }

basically, the first method retrieves the singleton instance of the HttpRuntime

then the second method goes and inserts private member values into 2 fields the app domain paths.

With a reflective language, it's not always necissary to break dependencies... although mutating private state like this could probably get you into a lot of 'trouble' and it's certainly not clean to look at!