RSPEC:预期与预期的区别

我这里有两种规格:

it 'is not an included preferred gender' do
  house.preferred_gender = 3
  is_expected.not_to be_valid
end

it 'is an included preferred gender' do
  house.preferred_gender = 2
  expect(house).to be_valid
end

我不明白的是如果我在第二个规范中替换 expect(house).to be_valid 对于 is_expected.to be_valid ,然后我的测试失败:

失败:

1) House preferred gender is an included preferred gender
     Failure/Error: is_expected.to be_valid
       expected #<House id: nil, rent: nil, deposit: nil, description: nil, preferred_gender: nil, created_at: nil, updated_at: nil, available_at: nil, user_id: nil, lease_length: nil, built_in: nil> to be valid, but got errors: User must exist, Rent can't be blank, Rent is not a number, Preferred gender can't be blank, Preferred gender is not included in the list, Available at can't be blank
     # ./spec/models/house_spec.rb:94:in `block (3 levels) in <main>'

Finished in 16.27 seconds (files took 3.02 seconds to load)
52 examples, 1 failure

为什么会这样? 提前多谢!