title: NoMethodError: undefined method count in rspec while testing my mailer
body: <p>I try to test my mailer, but I have an error on my <code>.count</code> ,
  Here is my <code>Mailer.rb</code></p>
  <pre><code>def prices_mailer(recipient, prices, sender)
      @sender = sender.fullname
      email = recipient.email
      @name = recipient.fullname
      @prices = prices
      @prices_count = @prices.count
  
  @subject = 'test'
  set_meta_data(__method__)
  mail(to:email, subject: @subject, from: sender)
  end
  </code></pre>
  <p>while I try to test with rspec this is what I'm doing</p>
  <pre><code>describe 'prices_mailer' do
      let(:price) { create(:price) }
      let(:recipient) { 'John.doe2@gmail.com' }
      let(:sender) { 'John.doe@gmail.com' }
      let(:mail) { described_class.prices_mailer(recipient, price, sender_email) }
  end
  
  it 'renders the headers' do
        expect(mail.subject).to eq('test')
  end
  </code></pre>
  <p>When I run the specs, I have the following error :
  <code>NoMethodError: undefined method count for #&lt;Price</code></p>
  <p>Is anyone knows how to fix that ?</p>