#296322 follow-up. It's extremely helpful when I remember to commit ALL files. :P

modules/simpletest/tests/actions_loop_test.info

+; $Id$
+name = Actions loop test
+description = Support module for action loop testing.
+package = Testing
+version = VERSION
+core = 7.x
+files[] = actions_loop_test.module
+hidden = TRUE

modules/simpletest/tests/actions_loop_test.install

+<?php
+// $Id$
+
+/**
+ * Implementation of hook_install().
+ */
+function actions_loop_test_install() {
+   db_update('system')
+    ->fields(array('weight' => 1))
+    ->condition('name', 'actions_loop_test')
+    ->execute();
+}

modules/simpletest/tests/actions_loop_test.module

+<?php
+// $Id$
+
+/**
+ * Implement hook_hook_info().
+ */
+function actions_loop_test_hook_info() {
+  return array(
+    'actions_loop_test' => array(
+      'watchdog' => array(
+        'run' => array(
+          'runs when' => t('When a message is logged'),
+        ),
+      ),
+    ),
+  );
+}
+
+/**
+ * Implement hook_watchdog().
+ */
+function actions_loop_test_watchdog(array $log_entry) {
+  // If the triggering actions are not explicitly enabled, abort.
+  if (empty($_GET['trigger_actions_on_watchdog'])) {
+    return;
+  }
+  // Get all the action ids assigned to the trigger on the watchdog hook's
+  // "run" event.
+  $aids = _trigger_get_hook_aids('watchdog', 'run');
+  // We can pass in any applicable information in $context. There isn't much in
+  // this case, but we'll pass in the hook name and the operation name as the
+  // bare minimum.
+  $context = array(
+    'hook' => 'watchdog',
+    'op' => 'run',
+  );
+  // Fire the actions on the associated object ($log_entry) and the context
+  // variable.
+  actions_do(array_keys($aids), $log_entry, $context);
+}
+
+/**
+ * Implement hook_init().
+ */
+function actions_loop_test_init() {
+  if (!empty($_GET['trigger_actions_on_watchdog'])) {
+    watchdog_skip_semaphore('actions_loop_test', 'Triggering action loop');
+  }
+}
+
+/**
+ * Implement hook_action_info().
+ */
+function actions_loop_test_action_info() {
+  return array(
+    'actions_loop_test_log' => array(
+      'description' => t('Write a message to the log.'),
+      'type' => 'system',
+      'configurable' => FALSE,
+      'hooks' => array(
+        'any' => TRUE,
+      )
+    ),
+  );
+}
+
+/**
+ * Write a message to the log.
+ */
+function actions_loop_test_log() {
+  $count = &drupal_static(__FUNCTION__, 0);
+  $count++;
+  watchdog_skip_semaphore('actions_loop_test', "Test log #$count");
+}
+
+/**
+ * Replacement of the watchdog() function that eliminates the use of semaphores
+ * so that we can test the abortion of an action loop.
+ */
+function watchdog_skip_semaphore($type, $message, $variables = array(), $severity = WATCHDOG_NOTICE, $link = NULL) {
+  global $user, $base_root;
+
+  // Prepare the fields to be logged
+  $log_entry = array(
+    'type'        => $type,
+    'message'     => $message,
+    'variables'   => $variables,
+    'severity'    => $severity,
+    'link'        => $link,
+    'user'        => $user,
+    'request_uri' => $base_root . request_uri(),
+    'referer'     => $_SERVER['HTTP_REFERER'],
+    'ip'          => ip_address(),
+    'timestamp'   => REQUEST_TIME,
+  );
+
+  // Call the logging hooks to log/process the message
+  foreach (module_implements('watchdog') as $module) {
+    module_invoke($module, 'watchdog', $log_entry);
+  }
+}