问题
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?
回答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.
回答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.
回答3:
The MyClassLibrary assembly was set to x86 mode in the configuration manager. Changing this to x64 fixed it. I really wish Visual Studio would detect this and report it as a less obscure error.
回答4:
Happened to me too. It is related to building for x64, Release and x86 mode. In my case, I deleted folders in my bin (debug/release/x86 in reference assemblies and unit test) and re-run my unit test. VS2010 somewhat reported the error in Output Window. That solved it for me.
回答5:
Came through this today and though I would leave my fix.
Specs: VS 2013 / .Net 4.0
Solution: Go into Menu > Test > Test Settings > Default Processor Architechture > X64
回答6:
It happened to me when i was trying to add test project with the same main project name.
My main project name was : Calculator.OperationsManager my test project name was : Calculator.OperationsManager
i have changed the test project name as Calculator.OperationsManager.Test and everything went well.
回答7:
Same message here, but I couldn't Debug the test either.
In my case, the DLL I was testing was deployed to the GAC (a BizTalk requirement). I had created a new class and was testing it, but hadn't GAC'd the DLL again since adding the class under test.
回答8:
In case this helps others with the same error (I realise it doesn't directly answer the question re Release vs Debug); I merged in a legacy project with a namespace that conflicted with an existing one, so renamed it. I got this error when trying to create a form from that project.
I checked the platform target was the same, and deleted the .\bin\ directories to ensure a clean rebuild, removed the reference to the merged project and re-added it, but still the same error.
Eventually (!) I checked the Assembly Name in the project's properties (right click on project, select 'properties', select the 'Application' tab) and changed that to match the Default namespace, and all is now well.
回答9:
I had similar problem as Trey, but instead of BizTalk, I have SharePoint solution which also uses GAC deployment. GAC had an older assembly. When I removed the GAC assembly by retracting the solution, the test passed.
回答10:
I had this error using NUnit 3 in VS 2013. I solved it by deleting the assembly reference in my test project for the assembly that contained the type that was not being found, and then re-added the reference.
回答11:
Just in case anyone needs this: I had created a test project in Visual Studio and had wondered why some Classes couldn't be found even if Visual Studio repeatedly asked me to add "System.Web" as reference.
I had done that and the error kept occurring. The problem for me was simple (and I should have checked that before, I know): I had created a test project from a template that created a .NET Core project. After changing it to .NET Framework 4.6.1 and adding "System.Web" as reference, everything worked fine.
回答12:
Encountered the same issue. Just in case if it helps anyone - I managed to get it to work by downgrading the nuget package NUnit3TestAdapter from version 3.13.0 to 3.11.2.
You can find more information on this - https://github.com/nunit/nunit-console/issues/424
来源：https://stackoverflow.com/questions/5735673/what-could-be-causing-a-system-typeloadexception-in-a-visual-studio-unit-test