add fonction empty for cerfa

spec/models/cerfa_spec.rb

@@ -9,4 +9,15 @@ describe Cerfa do
     it { is_expected.to belong_to(:dossier) }
   end
 
+  describe 'empty?' do
+    subject { create(:cerfa, content: content)}
+    context 'when content exist' do
+      let(:content) { File.open('./spec/support/files/piece_jointe_388.pdf') }
+      it { expect(subject).not_to be_empty }
+    end
+    context 'when content is nil' do
+      let(:content) { nil }
+      it { expect(subject).to be_empty }
+    end
+  end
 end