RSpec: difference between is_expect and expect

Question

I have two specs here:

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

What I don't understand is that if I replace in my second spec expect(house).to be_valid for is_expected.to be_valid, then my test fails:

Failures:

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

Why does this happen? Thanks a lot in advance!

Answer 1

is_expected is defined simply as expect(subject) and is designed for when you are using rspec-expectations with its newer expect-based syntax.

https://relishapp.com/rspec/rspec-core/docs/subject/one-liner-syntax

As the object under test is house not subject, I assume that subject is not initialized, therefore set to defaul (described_class.new). is_expected calls expectation on this default subject.

To use is_expected, initialize subject:

describe House do
   subject { House.new(...) } # or build :house if you use FactoryBot
   # ...
end