t/cdbi/09-has-many.t has a specific test for it.
my $self = shift;
my $rel = shift;
+ $self->throw_exception("Can't call *_related as class methods")
+ unless ref $self;
+
# we need to stop and check if this is at all possible. If this is
# an extended relationship with an incomplete definition, we should
# just forbid it right now.