Make it a bit easier to debug

gratipay/testing/browser.py

@@ -99,7 +99,7 @@ def wait_to_disappear(self, selector, timeout=2):
         while time.time() < end_time:
             if not self.has_element(selector):
                 return
-        raise NeverLeft()
+        raise NeverLeft(selector)
 
     def wait_for(self, selector, timeout=2):
         """Wait up to ``timeout`` seconds for element specified by ``selector``
@@ -109,7 +109,7 @@ def wait_for(self, selector, timeout=2):
         while time.time() < end_time:
             if self.has_element(selector):
                 return self.find_by_css(selector)
-        raise NeverShowedUp()
+        raise NeverShowedUp(selector)
 
     def wait_for_notification(self, type='notice'):
         """Wait for a certain ``type`` of notification. Dismiss the

tests/py/test_testing.py

@@ -0,0 +1,14 @@
+# -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
+
+import traceback
+
+from gratipay.testing.browser import NeverLeft
+
+
+def test_fail_repr():
+    try:
+        raise NeverLeft('.some.selector')
+    except:
+        formatted = traceback.format_exc()
+        assert 'NeverLeft: .some.selector' in formatted