--------------------
void foo()
{
    interface I { }
}
void bar()
{
    interface I { void foo(); }
    I i;
    i.foo();
}
--------------------
test.d(9): Error: no property 'foo' for type 'test.foo.I'
test.d(9): Error: function expected before (), not __error of type int
--------------------

The compiler uses foo.I instead of bar.I. This prevents me from using local interfaces inside unittests.

This does not happen with classes nor structs.