As numerous others are blogging about all that's done, I can concentrate on one thing: unit testing. As the unit testing plan on Drupal.org says

To perform unit testing each function needs to be isolated from all other functions. To do this all "sub calls" to other drupal functions need be located and each drupal function needs to be overridden to return a static value. The current plan is to use runkit.

. As we were discussing the how in Paris it hit me that we can do better: don't overwrite anything, instead create a skeleton-Drupal which copies all the functions but replaces the function body with a call to the test clearinghouse and then the clearinghouse can tell what's the current return value. I am unsure now who came up with the idea that when this script runs we can copy Drupal to an original-Drupal, where all functions are prefixed by original_. So we have functions like:

function variable_init($conf = array()) {
  return test_clearinghouse('variable_init', $conf);
}

and we also have:

function original_variable_init($conf = array()) {
  // NOTE: caching the variables improves performance by 20% when serving cached pages.
  if ($cached = cache_get('variables', 'cache')) {
...
}

Here is the beginning of the unit test for variable_init:

array(
    array(
      'incoming' => array('cache_get', 'variables', 'cache'),
      'return' => FALSE,
    ),
    array(
      'incoming' => array('db_query', 'SELECT * FROM {variable}'),
      'return' => '__test_placeholder__',
    ),
    array(
      'incoming' => array('db_fetch_object', '__test_placeholder__'),
      'return' => (object) array('name '=> 'foo', 'value' => serialize('bar')),
    ),
    array(
      'incoming' => array('db_fetch_object', '__test_placeholder__'),
      'return' => FALSE,
    ),
...
  );

So you just read the code flow and can create a test like this.

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