my $foo = Foo->new(one => 1);
is($foo->one, 1, 'ro reads');
-$foo->one(-3) unless $Method::Generate::Accessor::CAN_HAZ_XS;
+ok(exception { $foo->one(-3) }, 'ro dies on write attempt');
is($foo->one, 1, 'ro does not write');
is($foo->two, undef, 'rw reads');