NotificationMailer: add send notification

spec/mailers/notification_mailer_spec.rb

@@ -1,6 +1,16 @@
 require "spec_helper"
 
 RSpec.describe NotificationMailer, type: :mailer do
+  describe '.send_notification' do
+    let(:user) { create(:user) }
+    let(:dossier) { create(:dossier, user: user) }
+    let(:email) { instance_double('email', object_for_dossier: 'object', body_for_dossier: 'body') }
+    subject { described_class.send_notification(dossier, email) }
+
+    it { expect(subject.subject).to eq(email.object_for_dossier) }
+    it { expect(subject.body).to eq(email.body_for_dossier) }
+  end
+
   describe ".new_answer" do
     let(:user) { create(:user) }
     let(:dossier) { create(:dossier, user: user) }