thing_spec.rb

subject(:valid_things_ids) { described_class.valid_things_ids(group) }

let(:group) { 'example' }

before do
  described_class::VALID_THINGS.each do |thing|
    FactoryGirl.create(:something, group: 'example', name: thing)
  end
end

described_class::VALID_THINGS.each do |thing|
  it "contains things with the name #{thing}" do
    the_thing = described_class.find_by_group_and_name('example', thing)
    expect(valid_things_ids).to include the_thing.id
  end
end