-ok( $o->set( foo => 'bar' ), 'set foo' );
-cmp_ok( $o->get( 'foo' ), 'eq', 'bar', 'get foo' );
+ok( $o->set( foo => 'bar' ), 'set foo => bar' );
+
+eval { $o->set( foo => 'bar', 1 ) };
+ok( $@, 'set foo => bar new again failed' );
+
+cmp_ok( $o->get( 'foo' ), 'eq', 'bar', 'get foo = bar' );
+
+ok( $o->set( foo => 'baz' ), 'set foo => baz' );
+
+cmp_ok( $o->get( 'foo' ), 'eq', 'baz', 'get foo = baz' );