cat_spec.rb

# spec/models/cat_spec.rb
require 'rails_helper.rb'

RSpec.describe Cat, type: :model do
  # this is a test target model
  let(:cat) { Cat.new(status: status) }

  # this block describes Cat#nyan instance method
  # when you reference an instance method, write `Class#method`
  # and for a class method, write 'Class.method'
  describe '#nyan' do
    # this is the test target
    # and can be referenced as `subject`
    subject { cat.nyan }

    # and this block describes test conditions
    context 'When a cat is hungry' do
      # this is the first test condition
      let(:status) { :hungry }

      # and the expectation under the test condition
      it 'says nyaaaan' do
        expect(subject).to eq('nyaaaan')
      end
    end
  end
end