title: Preview devise mailer not found
body: <p>I try to have a preview of devise mailer but when it doesn't work.</p>
  
  <p>I have followed this <a href="https://guides.rubyonrails.org/action_mailer_basics.html#previewing-emails" rel="nofollow noreferrer">rails guide</a> and it doesn't seems difficult and many things to do.</p>
  
  <p>Devise already have a mailer class <a href="https://github.com/plataformatec/devise/blob/master/app/mailers/devise/mailer.rb" rel="nofollow noreferrer">here</a></p>
  
  <p>So I should only have to create a preview file so here is what I have done so far.</p>
  
  <p>I generated my devise views in the repository <code>app/views/users/mailer/</code></p>
  
  <p>I have my <code>devise.rb</code>which look like that </p>
  
  <pre><code>Devise.setup do |config|
  # ==&gt; Mailer Configuration
    # Configure the e-mail address which will be shown in Devise::Mailer,
    # note that it will be overwritten if you use your own mailer class
    # with default "from" parameter.
    config.mailer_sender = 'please-change-me-at-config-initializers-devise@example.com'
  
    # Configure the class responsible to send e-mails.
    config.mailer = 'Devise::Mailer'
    # Configure the parent class responsible to send e-mails.
    #config.parent_mailer = 'ActionMailer::Base'
  end
  </code></pre>
  
  <p>I have my <code>test/mailers/previews/devise_mailer_preview.rb</code></p>
  
  <pre><code>class DeviseMailerPreview&lt; ActionMailer::Preview
  
    def confirmation_instructions
      Devise::Mailer.confirmation_instructions(User.first, "faketoken")
    end
  
    def reset_password_instructions
      Devise::Mailer.reset_password_instructions(User.first, "faketoken")
    end
  
  end
  </code></pre>
  
  <p>I didn't change the path <code>config.action_mailer.preview_path</code>in my <code>application.rb</code> because <code>test/mailers/previews</code> is the default path</p>
  
  <p>So now when I try to access to <code>http://localhost:3000/rails/mailers</code> I have a white empty page
  and if I try <code>http://localhost:3000/rails/mailers/users/mailer/confirmation_instructions</code> I have this error <code>Mailer preview 'users/mailer/confirmation_instructions' not found</code></p>
  
  <p>I tried many different link but still have the same error, I also tried to followed this <a href="https://stackoverflow.com/a/25860079">stackoverflow answer</a> but no success.</p>
  
  <p>It's seems so easy but I can't succeed ...</p>