added a snippet to tell django/nose to not cover a function

UltiSnips/python.snippets

@@ -40,3 +40,7 @@ endsnippet
 snippet af "Assert false"
 self.assertFalse(${1:condition})
 endsnippet
+
+snippet nocover "Remove the block from the coverage"
+# pragma: no cover
+endsnippet