add empty to piece_jointe

spec/models/piece_jointe_spec.rb

@@ -27,4 +27,17 @@ describe PieceJointe do
       end
     end
   end
+
+  describe '#empty?' do
+    let(:piece_jointe) { create(:piece_jointe, content: content) }
+    subject { piece_jointe.empty? }
+    context 'when content is nil' do
+      let(:content) { nil }
+      it { is_expected.to be_truthy }
+    end
+    context 'when content exist' do
+      let(:content) { File.open('./spec/support/files/piece_jointe_388.pdf') }
+      it { is_expected.to be_falsey }
+    end
+  end
 end