What could be causing a System.TypeLoadException in a Visual Studio Unit Test?

Question

I've got a C# .NET class library MyClassLibrary that compiles fine. I'm trying to create a unit test project for it (using Visual Studio Unit Testing Framework, with Visual Studio 2010). The class library does have big classes in it, but whenever I run even the simplest test against the simplest class, I get the following exception:

Test method MyClassLibraryTest.MyClassLibraryTests.MySimpleClassTest threw exception: System.TypeLoadException: Could not load type 'MyClassLibrary.MySimpleClass' from assembly 'MyClassLibrary, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.

All of the projects I'm dealing with are in the same solution, and all are compiled for .NET 4.0. All of this is on a Windows 7 64-bit machine.

Here's the weird part: when I "Run" the test, I get the above error. But when I "Debug" the test, it runs fine. Why?

Answer 1

I just banged my head against this one for an hour. The problem was that I had a command line project named Something.exe, which was using a class library project named Something.dll.

Answer 2

Happened to me too. In my case the problem arised because the tested project and the unit tests project had the same name. If this is your case too then rename one of the projects and rename output file name to fix it.