Improve flaky form interaction process in #fill_in_tag

spec/support/request/web_helper.rb

@@ -137,7 +137,10 @@ module WebHelper
   end
 
   def fill_in_tag(tag_name, selector = "tags-input .tags input")
+    expect(page).to have_selector selector
+    find(:css, selector).send_keys ""
     find(:css, selector).set "#{tag_name}\n"
+    expect(page).to have_selector ".tag-list .tag-item span", text: tag_name
   end
 
   private