Writing cucumber/turnip steps that would as both "I should XYZ" and "I should not XYZ"

authentication_steps.rb

module AuthenticationSteps
  
  # Before, this required two steps, one for "should" and one for "should not".
  # Alternatively, you could write a single step that had a `:should` placeholder, 
  # but required an `if negated ... else ... end`, which still duplicated the matchers.

  step "I :should be on the main app page" do |negated|
    with_negation(negated) do
      expect(page).to have_current_path("/#")
      expect(page).to have_text(@authenticated_user.full_name)
    end
  end

  RSpec.configure { |c| c.include self }
end

placeholders.rb

module StepPlaceholders
  extend Turnip::DSL
  
  # order matters, longer regex goes first
  placeholder :should do
    match(/should not/) { true }
    match(/should/)     { false }
  end

  def with_negation(negated, &block)
    if negated
      begin
        swap_methods(::RSpec::Expectations::ExpectationTarget, :to, :not_to)
        yield
      ensure
        restore_methods(::RSpec::Expectations::ExpectationTarget, :to, :not_to)
      end
    else
      yield
    end
  end

  def swap_methods(mod, a, b)
    mod.module_exec do
      orig_a = :"__orig_#{a}"
      orig_b = :"__orig_#{b}"
      alias_method orig_a, a unless respond_to?(orig_a)
      alias_method orig_b, b unless respond_to?(orig_b)
      remove_method a
      remove_method b
      alias_method b, orig_a
      alias_method a, orig_b
    end
  end

  def restore_methods(mod, a, b)
    mod.module_exec do
      orig_a = :"__orig_#{a}"
      orig_b = :"__orig_#{b}"
      alias_method a, orig_a
      alias_method b, orig_b
    end
  end

  RSpec.configure { |c| c.include self }
end