Wednesday, 17 August 2011

System.BadImageFormatException with NUnit on 64bit Windows

This wasted a couple of hours until inspiration struck. In this case it was very useful to have a standalone app that ran the code through its paces without running unit tests.

I’d been developing tests for an x86-targeted library. The tests were fine on our 32bit workstations, but broke when we ran on our 64 bit build machine.

System.BadImageFormatException : Could not load file or assembly ‘XXX, Version=, Culture=neutral, PublicKeyToken=null' or one of its dependencies. An attempt was made to load a program with an incorrect format. 

Tests run on dev workstations went fine.

peverify for the assembly indicated that it was fine.

A simple app that just called LoadLibrary for the assembly indicated it was fine.

A sophisticated proprietary test app that ran the code through its paces behaved as expected.

Build machine was 64 bit OS, compared to 32 bit workstations. I assumed – because of the above – that the library was fine, so I couldn’t figure out why the test was failing. I couldn’t hit the right search on Google for it until it struck me that of course – it was just the nunit tests that were failing. Searching for:

nunit badimageformatexception 64 bit

immediately brought up a wealth of information. On 64 bit machines you need to run the specific x86-targeted nunit apps to test x86-targeted assemblies.

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