fix(dossier_transfer): require a valid email

Cf #7621

spec/controllers/users/transfers_controller_spec.rb

@@ -13,4 +13,33 @@ describe Users::TransfersController, type: :controller do
 
     it { expect { dossier_transfert.reload }.to raise_error(ActiveRecord::RecordNotFound) }
   end
+
+  describe "POST create" do
+    subject { post :create, params: { dossier_transfer: { email: email, dossier: dossier.id } } }
+
+    before { subject }
+
+    context "with valid email" do
+      let(:email) { "test@rspec.net" }
+
+      it { expect(DossierTransfer.last.email).to eq(email) }
+      it { expect(DossierTransfer.last.dossiers).to eq([dossier]) }
+    end
+
+    shared_examples 'email error' do
+      it { expect { subject }.not_to change { DossierTransfer.count } }
+      it { expect(flash.alert).to match([/invalide/]) }
+      it { is_expected.to redirect_to transferer_dossier_path(dossier.id) }
+    end
+
+    context "when email is empty" do
+      let(:email) { "" }
+      it_behaves_like 'email error'
+    end
+
+    context "when email is invalid" do
+      let(:email) { "not-an-email" }
+      it_behaves_like 'email error'
+    end
+  end
 end