In order to route a request like /test/something
to internally rewrite so that the content at /test.php?whatever=something
gets served, you would use these rules in the htaccess file in your document root:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^/?test/(.*?)/?$ /test.php?whatever=$1 [L]
And in order to redirect the query string URL to the nicer looking one:
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /test\.php\?whatever=([^\&\ ]+)
RewriteRule ^/?test\.php$ /test/%1? [L,R=301]