protected function I_can_ask_it_which_type_is_it(Skill $skill)
 {
     // should be only one type
     self::assertSame(1, $this->shouldBePhysical() + $this->shouldBePsychical() + $this->shouldBeCombined());
     self::assertSame($this->shouldBePhysical(), $skill->isPhysical());
     self::assertSame($this->shouldBePsychical(), $skill->isPsychical());
     self::assertSame($this->shouldBeCombined(), $skill->isCombined());
 }