unit_test_spec.rb

unit_test_spec.rb

class A
  def foo(num)
    %w[one two three][num - 1]
  end
end

describe A do
  describe "#foo" do
    RSpec::Matchers.define :do_foo do |args|
      match do |instance|
        instance.foo(args) == @expectation
      end

      chain :to do |expectation|
        @expectation = expectation
      end
    end

    subject(:instance) { A.new }

    it { should do_foo(1).to('one') }
    it { should do_foo(2).to('two') }
    it { should do_foo(3).to('three') }
  end
end