tests: make sure no ambiguities remains after the commit

This will help to stabilize part of the test that are not relevant for what is
actually tested.

Differential Revision: https://phab.mercurial-scm.org/D11778

tests/test-dirstate-race2.t

@@ -19,6 +19,12 b" outside of hg's control."
   $ hg commit -qAm _
   $ echo aa > a
   $ hg commit -m _
+# this sleep is there to ensure current time has -at-least- one second away
+# from the current time. It ensure the mtime is not ambiguous. If the test
+# "sleep" longer this will be fine.
+# It is not used to synchronise parallele operation so it is "fine" to use it.
+  $ sleep 1
+  $ hg status
 
   $ hg debugdirstate --no-dates
   n 644          3 (set  |unset)               a (re)