--- a/tests/test-topic.t	Wed Aug 30 17:32:32 2017 +0200
+++ b/tests/test-topic.t	Tue Aug 29 19:03:59 2017 +0530
@@ -90,6 +90,14 @@
   abort: cannot use --clear when setting a topic
   [255]
 
+Trying some invalid topicnames
+
+  $ hg topic '.'
+  $ hg topic null
+  $ hg topic tip
+  $ hg topic 12345
+  $ hg topic '   '
+
 Test commit flag and help text
 
   $ echo stuff >> alpha