CONTRIBUTING: Highlight request for test cases

CONTRIBUTING.md

@@ -123,12 +123,12 @@ guidelines in mind:
 
 - Please test your code thoroughly before sending it to us. We don't
   have access to all the commands for which we are sent completion
-  functions, so we are unable to test them all personally. If your code
-  is accepted into the distribution, a lot of people will try it out,
-  so try to do a thorough job of eradicating all the bugs before you
-  send it to us. If at all practical, add test cases to our test suite
-  (in the test/ dir) that verify that the code does what it is intended
-  to do, fixes issues it intends to fix, etc.
+  functions, so we are unable to test them all personally. If your
+  code is accepted into the distribution, a lot of people will try it
+  out, so try to do a thorough job of eradicating all the bugs before
+  you send it to us. If at all practical, **add test cases** to our
+  test suite (in the test/ dir) that verify that the code does what it
+  is intended to do, fixes issues it intends to fix, etc.
 
 - File bugs, enhancement, and pull requests at GitHub,
   https://github.com/scop/bash-completion