C# Uncaught exception in unit test

I'm encountering a very strange issue while debugging a unit test. If I debug the unit test (ctrl+r ctrl+t) I am getting an uncaught exception. If I just run the unit test (ctrl+r t) I do not get this exception.

The uncaught exception is a NHibernate.ByteCode.ProxyFactoryFactoryNotConfiguredException.

Stack trace:

at NHibernate.Bytecode.AbstractBytecodeProvider.get_ProxyFactoryFactory() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Bytecode\AbstractBy开发者_开发知识库tecodeProvider.cs:line 32
at NHibernate.Validator.Util.NHibernateHelper.IsProxyFactoryConfigurated()

I used .Net Reflector to look at the assembly that defines this method (NHibernate.Validator ... it's open source) and here is the method that "throws" the exception:

public static bool IsProxyFactoryConfigurated()
{
    try
    {
        IProxyFactoryFactory proxyFactoryFactory = Environment.BytecodeProvider.ProxyFactoryFactory;
        return true;
    }
    catch (ProxyFactoryFactoryNotConfiguredException)
    {
        return false;
    }
}

How can this exception not be caught by that Try Catch block?

It sounds like you're seeing a first chance exception.

Do you have "Break on first-chance exceptions" enabled? You should be able to configure it in the Debug->Exceptions menu.

You probably have Break on All Exceptions set in the debugger, which causes VS to break as soon as an exception is thrown, regardless of whether it's caught.
Click Debug, Exceptions.