.htaccess file works with Errors, but not with rewriting - php

Question

I've created a .htaccess file, and can get the server to serve me a custom 404 page. However, when i try and do a re-write, it doesn't work.
The htaccess file is located in the root directory.
RewriteEngine On
RewriteRule /htaccessTest/index.php /htaccessTest/phpinfo.php
ErrorDocument 404 /htaccessTest/errors/404_message.php
I'm not sure as to why this isn't working. I've checked phpinfo, and under Apache2, it states that mod_rewrite has been loaded.
I'm really stumped here. Not sure what's going on!
Any help would be great!
Update 1
As per what was highlighted below, i found that it still didn't work! I've made some changes, and now all I get is the 404 error message, unless I navigate to the index page.
Here are the changes:
ErrorDocument 404 /htaccessTest/errors/404_message.php
RewriteEngine On
RewriteRule ^htaccessTest/test\.php$ /htaccessTest/phpinfo\.php$ [L,NC]
And i access it using the url:
localhost/htaccessTest/test.php
(ignore the lack of http://, I've removed so that it didn't think it was a link).
Any further ideas?
Thanks

Answer 1

Try your rule without leading slash:
ErrorDocument 404 /htaccessTest/errors/404_message.php
RewriteEngine On
RewriteRule ^htaccessTest/index\.php$ /htaccessTest/phpinfo.php [L,NC]
Better to use line start/end anchors to avoid matching unexpected text in an URI.
dot needs to be escaped in a regex which otherwise matches any character.
.htaccess is per directory directive and Apache strips the current directory path (thus leading slash) from RewriteRule URI pattern.

Answer 2

Finally found the answer after hacking around with it.
It seems to be the first part of the Rewrite.
There is a difference with the first and second section that I didn't realise, which is that the URL sort of "resets" when using Rewrite.
This is explained easier by giving you the now re-worked example.
Original:
RewriteRule ^htaccessTest/test\.php$ /htaccessTest/phpinfo\.php$ [L,NC]
New:
RewriteRule ^test.php /htaccessTest/phpinfo.php
As you can see, the first part references htaccessTest. You don't need this part, as the url was "already in" this file structure. Your url being: "localhost/htaccessTest/test.php"
The second part stays roughly the same, I just removed the Regex stuff and the [L,NC]. The [L, NC] will probably come in handy later, but for simplicity sake I removed it.
The result is this:
ErrorDocument 404 /htaccessTest/errors/404_message.php
RewriteEngine On
RewriteRule ^test.php /htaccessTest/phpinfo.php
Thanks for the help guys! (Especially #anubhava)