Unit Testing, WCF and MEF – Part 2

In the first part of this article I showed how I’ve been testing code using MEF and a generic base class that is in charge of wiring up the dependencies.

In this part I will focus on how I got WCF to wire up my web service using MEF in what I think is quite an elegant way.

My first requirement was to be able to write a web service that will use dependencies (imports) but that wouldn’t require me to write the composition code in the service class itself. Most of the examples I saw online didn’t provide me with a good way to do that unfortunately.

Until I came across this excellent post by Tim Roberts which shows how to tap into the WCF pipe-line and have your services composed automatically instead of having to do it per service or including wire-up code in your classes.

While the code Tim provided was a great start I thought it wasn’t just right for me. Specifically it was the fact that it required custom code in the Global.asax file which for me was not as elegant as it should be.

So I’ve done a bit more digging into the WCF pipe-line and discovered that I could achieve an elegant, completely configuration-based solution by implementing my own endpoint behavior.

In the end I needed to only create 3 classes to achieve this: EndpointComposedElement, ComposedEndpointBehavior and ComposedInstanceProvider.

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Unit Testing, WCF and MEF


This article will focus on how I’ve adopted unit testing in .NET using MEF and how to also apply this to WCF web services.

I haven’t been dedicated to unit testing for a long time but once I started I couldn’t stop. There are many great benefits to doing unit tests, I wont list them here but a good article to read is at: Agitar.com

What made me build something on my own? I wanted something light that I could also integrate into existing code without making too many changes. So I focused on a couple of things: Testing and Dependency Injection. I wanted an elegant solution that didn’t rely on external libraries or that will require a steep learning-curve.

In this article I will focus on these topics and how I solved it for myself. I’m not going to dive into other topics such as The SOLID principals, TDD, Dependency Injection, Mocking, etc. If these terms are not familiar to you, I suggest you read up on them first.

I’m actually going to divide this article into two parts, to keep them shorter and to the point:

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