7.x 2.x Function: at_fn

Drupal code is function base structure. So it's very hard to override some Drupal's default functions, which leads to untestable code.

For example, if our class use l(), the function which perform SQL query to database, we can not write unit test for our class. We need way to override it, poorly, we can not do it nicely, we have to wrap the function call with at_fn() — use at_fn('l', $text, $path) instead of l($text, $path). Then, to override default l(), just call at_fn_fake('l', function($text, $path){ return '<a href="/'. $path .'">'. $text .'</a>'; })