Display Suite custom function field not firing
Here is the code that worked for me... My Module name is drup_custom

function drup_custom_ds_fields_info($entity_type)
{
    if ($entity_type != 'node') {
        return;
    }

    $fields = array();


    $fields['test_title'] = array(
        'title' =&gt; t('Split product title'),
        'field_type' =&gt; DS_FIELD_TYPE_FUNCTION,
        'function' =&gt; 'drup_custom_ds_field_splittitle'
    );


    return array('node' =&gt; $fields);

}

function drup_custom_ds_field_splittitle($field)
{
  return 'My Content';
}


Steps to follow to see results..


Cleared Caches
Enabled Layout in Content Type Settings





Now, you can see your field in disabled list





Assign the field to which ever region you would like, Save Settings





I can see the field content in Node View Page