diff --git a/lib/ajax/ajaxlib.php b/lib/ajax/ajaxlib.php
index c57e6c04014..c9f21f85344 100644
--- a/lib/ajax/ajaxlib.php
+++ b/lib/ajax/ajaxlib.php
@@ -67,3 +67,40 @@ function ajaxenabled(array $browsers = null) {
         return false;
     }
 }
+
+/**
+ * Starts capturing output whilst processing an AJAX request.
+ *
+ * This should be used in combination with ajax_check_captured_output to
+ * report any captured output to the user.
+ *
+ * @retrun Boolean Returns true on success or false on failure.
+ */
+function ajax_capture_output() {
+    // Start capturing output in case of broken plugins.
+    return ob_start();
+}
+
+/**
+ * Check captured output for content. If the site has a debug level of
+ * debugdeveloper set, and the content is non-empty, then throw a coding
+ * exception which can be captured by the Y.IO request and displayed to the
+ * user.
+ *
+ * @return Any output that was captured.
+ */
+function ajax_check_captured_output() {
+    global $CFG;
+
+    // Retrieve the output - there should be none.
+    $output = ob_get_contents();
+    ob_end_clean();
+
+    if ($CFG->debugdeveloper && !empty($output)) {
+        // Only throw an error if the site is in debugdeveloper.
+        throw new coding_exception('Unexpected output whilst processing AJAX request. ' .
+                'This could be caused by trailing whitespace. Output received: ' .
+                var_export($output, true));
+    }
+    return $output;
+}
diff --git a/lib/tests/ajaxlib_test.php b/lib/tests/ajaxlib_test.php
new file mode 100644
index 00000000000..9e80697b586
--- /dev/null
+++ b/lib/tests/ajaxlib_test.php
@@ -0,0 +1,113 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Code quality unit tests that are fast enough to run each time.
+ *
+ * @package    core
+ * @category   phpunit
+ * @copyright  2013 Andrew Nicols
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU Public License
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+class core_ajaxlib_testcase extends advanced_testcase {
+
+    protected function helper_test_clean_output() {
+        $this->resetAfterTest();
+
+        $result = ajax_capture_output();
+
+        // ob_start should normally return without issue.
+        $this->assertTrue($result);
+
+        $result = ajax_check_captured_output();
+        $this->assertEmpty($result);
+    }
+
+    protected function helper_test_dirty_output($expectexception = false) {
+        $this->resetAfterTest();
+
+        // Keep track of the content we will output.
+        $content = "Some example content";
+
+        $result = ajax_capture_output();
+
+        // ob_start should normally return without issue.
+        $this->assertTrue($result);
+
+        // Fill the output buffer.
+        echo $content;
+
+        if ($expectexception) {
+            $this->setExpectedException('coding_exception');
+            ajax_check_captured_output();
+        } else {
+            $result = ajax_check_captured_output();
+            $this->assertEquals($result, $content);
+        }
+    }
+
+    public function test_output_capture_normal_debug_none() {
+        // In normal conditions, and with DEBUG_NONE set, we should not receive any output or throw any exceptions.
+        set_debugging(DEBUG_NONE);
+        $this->helper_test_clean_output();
+    }
+
+    public function test_output_capture_normal_debug_normal() {
+        // In normal conditions, and with DEBUG_NORMAL set, we should not receive any output or throw any exceptions.
+        set_debugging(DEBUG_NORMAL);
+        $this->helper_test_clean_output();
+    }
+
+    public function test_output_capture_normal_debug_all() {
+        // In normal conditions, and with DEBUG_ALL set, we should not receive any output or throw any exceptions.
+        set_debugging(DEBUG_ALL);
+        $this->helper_test_clean_output();
+    }
+
+    public function test_output_capture_normal_debugdeveloper() {
+        // In normal conditions, and with DEBUG_DEVELOPER set, we should not receive any output or throw any exceptions.
+        set_debugging(DEBUG_DEVELOPER);
+        $this->helper_test_clean_output();
+    }
+
+    public function test_output_capture_error_debug_none() {
+        // With DEBUG_NONE set, we should not throw any exception, but the output will be returned.
+        set_debugging(DEBUG_NONE);
+        $this->helper_test_dirty_output();
+    }
+
+    public function test_output_capture_error_debug_normal() {
+        // With DEBUG_NORMAL set, we should not throw any exception, but the output will be returned.
+        set_debugging(DEBUG_NORMAL);
+        $this->helper_test_dirty_output();
+    }
+
+    public function test_output_capture_error_debug_all() {
+        // In error conditions, and with DEBUG_ALL set, we should not receive any output or throw any exceptions.
+        set_debugging(DEBUG_ALL);
+        $this->helper_test_dirty_output();
+    }
+
+    public function test_output_capture_error_debugdeveloper() {
+        // With DEBUG_DEVELOPER set, we should throw an exception.
+        set_debugging(DEBUG_DEVELOPER);
+        $this->helper_test_dirty_output(true);
+    }
+
+}