Refactor method to reply to comment in tests

We take the comment as a parameter instead of the user, since usually
people reply to comments and not to users.

We also remove one database query after the browser has started, since
we can use `debate_path(debate)`. It's also more clear why we're using
`debate_path` in the test; before these changes, we had to enter the
`reply_to` method to realize that we were replying on a debate.

spec/support/common_actions/comments.rb

@@ -6,12 +6,10 @@ module Comments
     CommentNotifier.new(comment: comment).process
   end
 
-  def reply_to(original_user, replier: create(:user))
-    debate  = create(:debate)
-    comment = create(:comment, commentable: debate, user: original_user)
-
+  def reply_to(comment, replier: create(:user))
     login_as(replier)
-    visit debate_path(debate)
+
+    visit polymorphic_path(comment.commentable)
 
     click_link "Reply"
     within "#js-comment-form-comment_#{comment.id}" do

spec/system/emails_spec.rb

@@ -177,27 +177,29 @@ describe "Emails" do
 
   context "Comment replies" do
     let(:user) { create(:user, email_on_comment_reply: true) }
+    let(:debate) { create(:debate) }
+    let!(:comment) { create(:comment, commentable: debate, user: user) }
 
     scenario "Send email on comment reply" do
-      reply_to(user)
+      reply_to(comment)
 
       email = open_last_email
       expect(email).to have_subject("Someone has responded to your comment")
       expect(email).to deliver_to(user)
-      expect(email).not_to have_body_text(debate_path(Comment.first.commentable))
+      expect(email).not_to have_body_text(debate_path(debate))
       expect(email).to have_body_text(comment_path(Comment.last))
       expect(email).to have_body_text("To stop receiving these emails change your settings in")
       expect(email).to have_body_text(account_path)
     end
 
     scenario "Do not send email about own replies to own comments" do
-      reply_to(user, replier: user)
+      reply_to(comment, replier: user)
       expect { open_last_email }.to raise_error("No email has been sent!")
     end
 
     scenario "Do not send email about comment reply unless set in preferences" do
       user.update!(email_on_comment_reply: false)
-      reply_to(user)
+      reply_to(comment)
       expect { open_last_email }.to raise_error("No email has been sent!")
     end
   end