test.rb

class Errorable
  attr_accessor :state, :errors

  def initialize(state)
    @state = state
    @errors = []
  end

  def method_missing(symbol, *args)
    raise NoMethodError, "undefined method `#{symbol}' for #{self}" unless self.respond_to?(symbol, true)
    return false unless ok?

    self.send(symbol, *args)
  end

  def ok?
    @errors.empty?
  end

  private
  def validate_params(params)
    if params[:greeting] == "Hello"
      true
    else
      @errors << "greeting must be 'Hello'"
      false
    end
  end

  def get_lesson_type
    if state[:lesson_type_id]
      lesson_type = "This lesson here"
      state[:lesson_type] = lesson_type
      return lesson_type
    else
      @errors << "Lesson type ID not found"
      return nil
    end
  end
end

errorable = Errorable.new({lesson_type_id: nil})
errorable.validate_params({greeting: "Hello"})
lesson_type = errorable.get_lesson_type

puts "errorable.ok => #{errorable.ok?.inspect}"
puts "errorable.state => #{errorable.state.inspect}"
puts "errorable.errors => #{errorable.errors.inspect}"