diff --git a/includes/ajax.inc b/includes/ajax.inc
index 0cd6f63e698f7fa8debb4e6cd67f648e00e81fa2..2701cb0ab1e887aeb3640264e3eb3b8b214a122a 100644
--- a/includes/ajax.inc
+++ b/includes/ajax.inc
@@ -142,7 +142,7 @@ function ajax_render($commands = array(), $header = TRUE) {
   // them the first command.
   $scripts = drupal_add_js(NULL, NULL);
   if (!empty($scripts['settings'])) {
-    array_unshift($commands, ajax_command_settings($scripts['settings']['data']));
+    array_unshift($commands, ajax_command_settings(call_user_func_array('array_merge_recursive', $scripts['settings']['data'])));
   }
 
   // Allow modules to alter any AJAX response.
@@ -156,7 +156,7 @@ function ajax_render($commands = array(), $header = TRUE) {
     // http://malsup.com/jquery/form/#code-samples
     print '<textarea>' . drupal_json_encode($commands) . '</textarea>';
   }
-  else if ($header) {
+  elseif ($header) {
     drupal_json_output($commands);
   }
   else {
@@ -773,7 +773,7 @@ function ajax_command_css($selector, $argument) {
 function ajax_command_settings($argument) {
   return array(
     'command' => 'settings',
-    'argument' => $argument,
+    'settings' => $argument,
   );
 }
 
diff --git a/modules/simpletest/simpletest.info b/modules/simpletest/simpletest.info
index 5e49bfb966f33d331e4e1c18c0eb1fda90ba15ab..1eb85d98a2b7e68f79f366c2ed75f1cbfc46c825 100644
--- a/modules/simpletest/simpletest.info
+++ b/modules/simpletest/simpletest.info
@@ -12,6 +12,7 @@ files[] = drupal_web_test_case.php
 
 ; Tests in tests directory.
 files[] = tests/actions.test
+files[] = tests/ajax.test
 files[] = tests/batch.test
 files[] = tests/bootstrap.test
 files[] = tests/browser.test
diff --git a/modules/simpletest/tests/ajax.test b/modules/simpletest/tests/ajax.test
new file mode 100644
index 0000000000000000000000000000000000000000..3a55dbb971451ab3ccc6ea5ded00cc4ab49787ff
--- /dev/null
+++ b/modules/simpletest/tests/ajax.test
@@ -0,0 +1,80 @@
+<?php
+// $Id$
+
+class AJAXTestCase extends DrupalWebTestCase {
+  function setUp() {
+    parent::setUp('ajax_test');
+  }
+
+  function drupalGetAJAX($path, $query = array()) {
+    $this->drupalGet($path, array('query' => $query));
+    return json_decode($this->content, TRUE);
+  }
+}
+
+/**
+ * Tests primary AJAX framework functions.
+ */
+class AJAXFrameworkTestCase extends AJAXTestCase {
+  function getInfo() {
+    return array(
+      'name' => 'AJAX framework',
+      'description' => 'Performs tests on AJAX framework functions.',
+      'group' => 'AJAX',
+    );
+  }
+
+  /**
+   * Test proper passing of JavaScript settings via ajax_render().
+   */
+  function testAJAXRender() {
+    $result = $this->drupalGetAJAX('ajax-test/render');
+    // Verify that JavaScript settings are contained (always first).
+    $this->assertIdentical($result[0]['command'], 'settings', t('drupal_add_js() settings are contained first.'));
+    // Verify that basePath is contained in JavaScript settings.
+    $this->assertEqual($result[0]['settings']['basePath'], base_path(), t('Base path is contained in JavaScript settings.'));
+  }
+
+  /**
+   * Test behavior of ajax_render_error().
+   */
+  function testAJAXRenderError() {
+    $result = $this->drupalGetAJAX('ajax-test/render-error');
+    // Verify default error message.
+    $this->assertEqual($result[0]['command'], 'alert', t('ajax_render_error() invokes alert command.'));
+    $this->assertEqual($result[0]['text'], t('An error occurred while handling the request: The server received invalid input.'), t('Default error message is output.'));
+    // Verify custom error message.
+    $edit = array(
+      'message' => 'Custom error message.',
+    );
+    $result = $this->drupalGetAJAX('ajax-test/render-error', $edit);
+    $this->assertEqual($result[0]['text'], $edit['message'], t('Custom error message is output.'));
+  }
+}
+
+/**
+ * Tests AJAX framework commands.
+ */
+class AJAXCommandsTestCase extends AJAXTestCase {
+  function getInfo() {
+    return array(
+      'name' => 'AJAX commands',
+      'description' => 'Performs tests on AJAX framework commands.',
+      'group' => 'AJAX',
+    );
+  }
+
+  /**
+   * Test ajax_command_settings().
+   */
+  function testAJAXRender() {
+    $commands = array();
+    $commands[] = ajax_command_settings(array('foo' => 42));
+    $result = $this->drupalGetAJAX('ajax-test/render', array('commands' => $commands));
+    // Verify that JavaScript settings are contained (always first).
+    $this->assertIdentical($result[0]['command'], 'settings', t('drupal_add_js() settings are contained first.'));
+    // Verify that the custom setting is contained.
+    $this->assertEqual($result[1]['settings']['foo'], 42, t('Custom setting is output.'));
+  }
+}
+
diff --git a/modules/simpletest/tests/ajax_test.info b/modules/simpletest/tests/ajax_test.info
new file mode 100644
index 0000000000000000000000000000000000000000..0d9c32a465907c6aab4a1bbdabdd464fe70a6f3f
--- /dev/null
+++ b/modules/simpletest/tests/ajax_test.info
@@ -0,0 +1,8 @@
+; $Id$
+name = AJAX Test
+description = Support module for AJAX framework tests.
+package = Testing
+version = VERSION
+core = 7.x
+files[] = ajax_test.module
+hidden = TRUE
diff --git a/modules/simpletest/tests/ajax_test.module b/modules/simpletest/tests/ajax_test.module
new file mode 100644
index 0000000000000000000000000000000000000000..27bf3bf169183d62607b3a7ededfcecd8063b678
--- /dev/null
+++ b/modules/simpletest/tests/ajax_test.module
@@ -0,0 +1,59 @@
+<?php
+// $Id$
+
+/**
+ * @file
+ * Helper module for AJAX framework tests.
+ */
+
+/**
+ * Implement hook_menu().
+ */
+function ajax_test_menu() {
+  $items['ajax-test/render'] = array(
+    'title' => 'ajax_render',
+    'page callback' => 'ajax_test_render',
+    'access callback' => TRUE,
+    'type' => MENU_CALLBACK,
+  );
+  $items['ajax-test/render-error'] = array(
+    'title' => 'ajax_render_error',
+    'page callback' => 'ajax_test_render_error',
+    'access callback' => TRUE,
+    'type' => MENU_CALLBACK,
+  );
+  return $items;
+}
+
+/**
+ * Menu callback; Copies $_GET['commands'] into $commands and ajax_render()s that.
+ *
+ * Additionally ensures that ajax_render() incorporates JavaScript settings
+ * by invoking drupal_add_js() with a dummy setting.
+ */
+function ajax_test_render() {
+  // Prepare AJAX commands.
+  $commands = array();
+  if (!empty($_GET['commands'])) {
+    $commands = $_GET['commands'];
+  }
+  // Add a dummy JS setting.
+  drupal_add_js(array('ajax' => 'test'), 'setting');
+
+  // Output AJAX commands and end the request.
+  ajax_render($commands);
+}
+
+/**
+ * Menu callback; Invokes ajax_render_error().
+ *
+ * Optionally passes $_GET['message'] to ajax_render_error().
+ */
+function ajax_test_render_error() {
+  $message = '';
+  if (!empty($_GET['message'])) {
+    $message = $_GET['message'];
+  }
+  ajax_render_error($message);
+}
+