Why isn't my hook_theme being called or rendering output? I am trying to use the hook_theme function to utilize some template files.  I have the following function defined in my theme:

template.php

function my_name_theme($existing, $type, $theme, $path) {
    return array(
        'testy' =&gt; array(
            'variables' =&gt; array('title' =&gt; NULL),
            'template'  =&gt; 'testy',
        ),
    );
}


And I have the following template defined:

testy.tpl.php

&lt;h1&gt;&lt;?php print $title; ?&gt;&lt;/h1&gt;


I have a content type called "Page" with a corresponding template:

node--page.tpl.php

&lt;?php
    print 'before theme call';
    $variables = array();
    $variables['title'] = 'my title';
    print theme('testy', $variables);
    print 'after theme call';
?&gt;


When viewing one of my "Page" content types, the rendered page only shows the following, with no title:

before theme callafter theme call

I have cleared all caches.  Why isn't this working?
I had to add a path to my function, then it worked.

template.php

function my_name_theme($existing, $type, $theme, $path) {
    return array(
        'testy' =&gt; array(
            'variables' =&gt; array('title' =&gt; NULL),
            'template'  =&gt; 'testy',
            'path'      =&gt; drupal_get_path('theme', 'my_name') . '/templates',
        ),
    );
}