extension to unittests

[BCS]

Here is somthing I'd like to be able to do with unittests

class Foo
{
  // stuff
  unittest(Foo function() dg)
  {
     Foo foo = dg();
     // do unittest on foo
  }
}


class Bar : Foo
{
  // Foo.unittest({return new Bar;}) gets run
}


I'm not sure how to handle issues about constructor variables (maybe some 
sort of opFactory or something)

another syntax that occurs to me would be to make the unittest a template 
that get specialized on an each of the derived types.

I'm not  to interested in the exact implementation but what I'm thinking 
of is the ability to enforce the Liskov substitution principle for classes 
(and preferably interfaces)