Is it possible to mock (via NSubstitute) an IList.PnPContext?

[Amwins-Vault-Boy]

I'm attempting to mock the PnPContext of an IList, but this is failing:

var accountDocumentLibraryList = Substitute.For<IList>();
accountDocumentLibraryList.Id.Returns(Guid.NewGuid());
accountDocumentLibraryList.Title.Returns(accountIdMock.ToString(CultureInfo.InvariantCulture));
accountDocumentLibraryList.Description.Returns(accountNameMock);

var pnpContextMock = Substitute.For<IPnPContext>();
pnpContextMock.Site.Id.Returns(Guid.NewGuid());
pnpContextMock.Web.Id.Returns(Guid.NewGuid());

accountDocumentLibraryList.PnPContext.Returns(pnpContextMock);

with this error:
NSubstitute.Exceptions.CouldNotSetReturnDueToTypeMismatchException : Can not return value of type ObjectProxy_6 for IDataModelWithContext.get_PnPContext (expected type PnPContext).

Is this at all possible to do? and, if so, what should I change to make this work?

Thanks for any suggestions and help!