title: Ruby on Rails 4: valid? always returns true
body: <p>I'm trying to use validators on my class, to validate information on my API. But it always returns true, when I call valid?</p>
  
  <p>Do you have any idea why? I'm using Rails 4.</p>
  
  <pre><code>class Address
     include ActiveModel::Model
     include ActiveModel::Validations
     include ActiveModel::AttributeMethods
  
     attr_accessor :street
  
     validates :street, length: { minimum: 10, maximum: 100 }
  end
  
  address = Address.new
  address.street = 'aa'
  address.valid? (returns true)
  </code></pre>