Troubleshooting Apache .htaccess mod_rewrite rules

I found this tip very useful in helping to diagnose a problem I had with a RewriteRule directive on my website.  Set up a RewriteRule for a non-existent page and redirect it to a known external site (e.g. http://www.google.com).  Type in the url to the .htaccess file path, include the name of the non-existent file, and see if the redirect works.