Can't create mocks of sealed classes

gistfile1.txt

public class ListOfAValidAndAInvalidRequirement {
	OnEstablish context =
		fakeAccessor =>
			{
				IRequirement validRequirement = fakeAccessor.An<IRequirement>();
				validRequirement.WhenToldTo(r => r.Validate()).Return(true); // throws ex here
				IRequirement invalidRequirement = fakeAccessor.An<IRequirement>();
				invalidRequirement.WhenToldTo(r=>r.Validate()).Return(false);
				IList<IRequirement> requirements = new List<IRequirement>
					                                {
					                                   	validRequirement,
														invalidRequirement
					                                };
				fakeAccessor.Configure(config => config.For<IList<IRequirement>>().Use(()=>requirements));
			};
}

public interface IRequirement {
	bool Validate();
}

throws "Can't create mocks of sealed classes"

gistfile2.cs

the complete spec:

public class When_validating_a_valid_requirement_and_a_invalid_requirement : WithSubject<RequirementsValidator>
{
	static bool _isValid;
	Establish context = () => { With<ListOfAValidAndAInvalidRequirement>(); };

	Because of = () => { _isValid = Subject.Validate(); };

	It should_not_be_valid = () => { _isValid.ShouldBeFalse(); };
}

public class ListOfAValidAndAInvalidRequirement {
	OnEstablish context =
		fakeAccessor =>
			{
				IRequirement validRequirement = fakeAccessor.An<IRequirement>();
				validRequirement.WhenToldTo(r => r.Validate()).Return(true);
				IRequirement invalidRequirement = fakeAccessor.An<IRequirement>();
				invalidRequirement.WhenToldTo(r=>r.Validate()).Return(false);
				IList<IRequirement> requirements = new List<IRequirement>
					                                {
					                                   	validRequirement,
														invalidRequirement
					                                };
				fakeAccessor.Configure(config => config.For<IList<IRequirement>>().Use(()=>requirements));
			};
}

public class RequirementsValidator {
	readonly IList<IRequirement> _requirements;

	public RequirementsValidator(IList<IRequirement> requirements) {
		_requirements = requirements;
	}

	public bool Validate() {
		return _requirements.Where(r => r.Validate()).Count() == _requirements.Count;
	}
}

public interface IRequirement {
	bool Validate();
}				                                   	

Ok, I'm going to try that with the merged mfakes assembly

While not getting the exception - does the test turn red or green?
Thanks for investigation, though.
Will have to dig into a test I wrote yesterday against the latest code base where I also used Configure and IList in BehaviorConfigs - weird stuff ;-)

So in all cases I tried Moq/Rhino/FakeItEasy --> merged/unmerged I didn't run into the exception. The specification fails because IList<IRequirement> contains no elements (explanation above ;-().

Maybe you did enable "Just my Code" in Debugging options?

This was enabled, however disabling it didn't change the outcome

Ok, could isolate it a little bit more:
using:
Subject = new RequirementsValidator(The<IList<IRequirement>>());
everything works fine - including BCs and Configure from above code

When letting Machine.Fakes inject The<IList<IRequirement>>() the exception is thrown.