Thursday, November 29, 2007

A Solution for Assembly Version Issue

Continuing with the issue I described in Rhino.Mocks and AutoMockingContainer, I found another solution to resolve the problem instead of recompiling AutoMockingContainer.

It is not always the case that you can get dependent library source codes. The alternative solution to redirect the .Net CLR to load a new version of the specified assembly. I'll take the my test project with Rhino.Mocks and AutoMockingContainer as an example. The Rhino.Mocks version I used in my project is version, while AutoMockingContainer was built with Rhino.Mocks version as its dependency. My test project will be compiled as TestClasses.dll. By default, all the binaries will be copied to Output directory with the latest Rhino.Mocks (

When my test class tries to call any AutoMockingContainer class which depends on Rhino.Mocks (, the .Net CLR cannot find the specified strong named assembly dll, and then exception was thrown.

I remembered that when .Net was released, it claimed to resolve COM-hell issue with versions and it allows two or more different versions of assembly running within a process. One way to resolve the version issue is to promote the version by using assembly's configuration file. For more information about .Net configuration, see Configuration File Schema for the .NET Framework.

That link provides a way to redirect old version to new version by using configuration's bindingRedirect element. Here is what I did in my test project:

  1. Add a configuration file to the project where AutoMockingContainer is referenced. The file name should be as same as the project name with congif extension. For example, I used "TestClasses.dll.config".

  2. Right click on this file and set Copy to Output Directory to Copy Always.

  3. Add the following line to the configuration file (make changes depending on your case):

<?xml version="1.0" encoding="utf-8" ?>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<assemblyIdentity name="Rhino.Mocks"
culture="neutral" />
<bindingRedirect oldVersion=""

  1. Finally compile the project. The project should run (with NUnit test program) without exception.

I used the tool of Lutz' .Net Reflector to find assembly's version. It's a great tool for developers.