The basic functionality of module_list().
function testModuleList() {
  // Build a list of modules, sorted alphabetically.
  $profile_info = install_profile_info('standard', 'en');
  $module_list = $profile_info['dependencies'];
  // Installation profile is a module that is expected to be loaded.
  $module_list[] = 'standard';
  sort($module_list);
  // Compare this list to the one returned by module_list(). We expect them
  // to match, since all default profile modules have a weight equal to 0
  // (except for block.module, which has a lower weight but comes first in
  // the alphabet anyway).
  $this
    ->assertModuleList($module_list, t('Standard profile'));
  // Try to install a new module.
  module_enable(array(
    'contact',
  ));
  $module_list[] = 'contact';
  sort($module_list);
  $this
    ->assertModuleList($module_list, t('After adding a module'));
  // Try to mess with the module weights.
  module_set_weight('contact', 20);
  // Reset the module list.
  system_list_reset();
  // Move contact to the end of the array.
  unset($module_list[array_search('contact', $module_list)]);
  $module_list[] = 'contact';
  $this
    ->assertModuleList($module_list, t('After changing weights'));
  // Test the fixed list feature.
  $fixed_list = array(
    'system' => array(
      'filename' => drupal_get_path('module', 'system'),
    ),
    'menu' => array(
      'filename' => drupal_get_path('module', 'menu'),
    ),
  );
  module_list(NULL, $fixed_list);
  $new_module_list = array_combine(array_keys($fixed_list), array_keys($fixed_list));
  $this
    ->assertModuleList($new_module_list, t('When using a fixed list'));
  // Reset the module list.
  module_list_reset();
  $this
    ->assertModuleList($module_list, t('After reset'));
}