I observed will be able to produce a blank file during my Wordpress theme, and employ a function I have produced in functions.php without including anything.

How's this possible?

My function in functions.php (

    function getContentFromID($int) {

        $my_id = $int;
        $my_id = get_post($my_id);
        $content = $my_id->post_content;
        $content = apply_filters('the_content', $content);
        $content = str_replace(']]>', ']]>', $content);
        echo $content;
}

ONLY content in test.php (also it will get the right content basically replace $scrapeID with e.g. 135)

<?php getContentFromID($scrapeID); ?>

Wordpress instantly include function.php within the template. see http://codex.wordpress.org/Theme_Development

By setting auto_prepend_file, you'll be able to incorporate a PHP apply for every PHP file.

Another thing has incorporated functions.php before test.php continues to be incorporated. PHP puts everything in one global scope unless of course you know it otherwise in some way.

Since your new file is incorporated by another file, which file including your file includes the functions file, therefore the functions are visible for your file.