setting template file using template_preproccess_page not working
Assuming D6 then, in template.php:

/**
 * Implements hook_preprocess_page
 */
function THEMENAME_preprocess_page(&amp;$variables){  
 if (strpos($_GET['q'], 'value/abc') === 0) {
   $variables['template_file'] = 'testing';
 }
}


Clear theme registry, or all caches at admin &gt; config &gt; performance to apply.

More info:


  There are two special variables that these hooks can set:
  'template_file' and 'template_files'. These will be merged together to
  form a list of 'suggested' alternate template files to use, in reverse
  order of priority. template_file will always be a higher priority than
  items in template_files. theme() will then look for these files, one
  at a time, and use the first one that exists.
  https://api.drupal.org/api/drupal/includes%21theme.inc/function/theme/6