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[mark cortes <680735@xxxxxxxxxxxxxxxxxx>]

Now, I understand. Thank you. Running the assemblies in separate AppDomains 
causes the correct assemblies to be loaded; however, the leaf nodes for some of 
the assemblies don't update and remain gray after the test runs. That should 
probably be reported as a separate bug. Still, I think the reference assemblies 
should only be searched for in the path of whichever assembly is being tested.

-- 
Failed tests: Could not load file or assembly
https://bugs.launchpad.net/bugs/680735
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Status in NUnit V2 Test Framework: New

Bug description:
NUNIT VERSION
NUnit 2.5.7.10213

DESCRIPTION
When multiple test assemblies are loaded into NUnit, and they reference different strongly named assemblies with the same file name, all but the first assembly fails all tests. The tests fail indicating the following exception was thrown:

NUnitTests.Common.ByteExtensionsTests.HighNibble:
System.IO.FileLoadException : Could not load file or assembly 'NLib, Version=1.1.0.0, Culture=neutral, PublicKeyToken=16fb73b766f2d210' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

PROBABLE CAUSE
By using fuslogvw.exe and reading about Microsoft's assembly loader, I have concluded the following: When Microsoft's assembly loader is searching for an assembly, it stops looking on the first directory containing an assembly with the correct file name. If the found assembly differs by version number or PublicKeyToken, a FileLoadException is thrown instead of looking further. This is apparently by design by Microsoft for performance reasons, although unintuitive. NUnit appears to cause the test assembly to search for referenced assemblies in the directories of ALL loaded test assemblies, and in the same order. Thus, the wrong assembly is used from the wrong directory. Under the unlikely case the referenced assemblies weren't strongly named, no error would be thrown indicating the wrong library is being tested.

SIGNIFICANCE
Using assemblies with identical names is useful when creating libraries to target multiple .NET Framework versions. NUnit 2.5.7 is unusable as a means to test the assemblies simultaneously, and it becomes necessary to test each piece of the final solution separately.