Use JavaScript in tests opening modal dialogs

This way we reproduce the user experience in the tests, and we can make
sure modal dialogs open when we expect it.

spec/system/emails_spec.rb

@@ -365,7 +365,7 @@ describe "Emails" do
       expect(email).to have_body_text(budget_path(budget))
     end
 
-    scenario "Unfeasible investment" do
+    scenario "Unfeasible investment", :js do
       budget.update!(phase: "valuating")
       valuator = create(:valuator)
       investment = create(:budget_investment, author: author, budget: budget, valuators: [valuator])
@@ -375,7 +375,7 @@ describe "Emails" do
 
       within_fieldset("Feasibility") { choose "Unfeasible" }
       fill_in "Feasibility explanation", with: "This is not legal as stated in Article 34.9"
-      check "Valuation finished"
+      accept_confirm { check "Valuation finished" }
       click_button "Save changes"
 
       expect(page).to have_content "Dossier updated"
@@ -478,6 +478,8 @@ describe "Emails" do
 
       click_link "Send"
 
+      expect(page).to have_content "Newsletter sent successfully"
+
       expect(unread_emails_for(user_with_newsletter_in_segment_1.email).count).to eq 1
       expect(unread_emails_for(user_with_newsletter_in_segment_2.email).count).to eq 1
       expect(unread_emails_for(user_with_newsletter_not_in_segment.email).count).to eq 0