diff --git a/lib/classes/progress/display.php b/lib/classes/progress/display.php
index b7974bc0b56..317e57ce647 100644
--- a/lib/classes/progress/display.php
+++ b/lib/classes/progress/display.php
@@ -38,7 +38,7 @@ class display extends base {
      */
     private $bar;
 
-    private $lastwibble, $currentstate = 0, $direction = 1;
+    protected $lastwibble, $currentstate = 0, $direction = 1;
 
     /**
      * @var bool True to display names
@@ -127,6 +127,12 @@ class display extends base {
                     $this->currentstate += 2 * $this->direction;
                 }
                 $buffersize = ini_get('output_buffering');
+                if (!is_numeric($buffersize)) {
+                    // The output_buffering setting can be a number, but can also be "On" or "Off".
+                    // If "Off", there's no buffer, if "On", there's no limit to the size. In either case,
+                    // there's no point in trying to fill the buffer.
+                    $buffersize = 0;
+                }
                 if ($buffersize) {
                     // Force the buffer full.
                     echo str_pad('', $buffersize);
diff --git a/lib/tests/progress_display_test.php b/lib/tests/progress_display_test.php
new file mode 100644
index 00000000000..8da0e781ded
--- /dev/null
+++ b/lib/tests/progress_display_test.php
@@ -0,0 +1,104 @@
+<?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/>.
+/**
+ *
+ *
+ * @package
+ * @copyright  2016 The Open University
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+defined('MOODLE_INTERNAL') || die();
+
+class progress_display_test extends \advanced_testcase {
+
+    /**
+     * Test basic function of progress_display, updating status and outputting wibbler.
+     */
+    public function test_progress_display_update() {
+        ob_start();
+        $progress = new core_mock_progress_display();
+        $progress->start_progress('');
+        $this->assertEquals(1, $progress->get_current_state());
+        $this->assertEquals(1, $progress->get_direction());
+        $this->assertTimeCurrent($progress->get_last_wibble());
+        // Wait 1 second to ensure that all code in update_progress is run.
+        sleep(1);
+        $progress->update_progress();
+        $this->assertEquals(2, $progress->get_current_state());
+        $this->assertEquals(1, $progress->get_direction());
+        $this->assertTimeCurrent($progress->get_last_wibble());
+        $output = ob_get_clean();
+        $this->assertContains('wibbler', $output);
+        $this->assertContains('wibble state0', $output);
+        $this->assertContains('wibble state1', $output);
+    }
+
+    /**
+     * Test wibbler states. Wibbler should reverse direction at the start and end of its sequence.
+     */
+    public function test_progress_display_wibbler() {
+        ob_start();
+        $progress = new core_mock_progress_display();
+        $progress->start_progress('');
+        $this->assertEquals(1, $progress->get_direction());
+
+        // Set wibbler to final state and progress to check that it reverses direction.
+        $progress->set_current_state(core_mock_progress_display::WIBBLE_STATES);
+        sleep(1);
+        $progress->update_progress();
+        $this->assertEquals(core_mock_progress_display::WIBBLE_STATES - 1, $progress->get_current_state());
+        $this->assertEquals(-1, $progress->get_direction());
+
+        // Set wibbler to beginning and progress to check that it reverses direction.
+        $progress->set_current_state(0);
+        sleep(1);
+        $progress->update_progress();
+        $this->assertEquals(1, $progress->get_current_state());
+        $this->assertEquals(1, $progress->get_direction());
+        $output = ob_get_clean();
+        $this->assertContains('wibbler', $output);
+        $this->assertContains('wibble state0', $output);
+        $this->assertContains('wibble state13', $output);
+
+    }
+
+}
+
+/**
+ * Helper class that allows access to private values
+ */
+class core_mock_progress_display extends \core\progress\display {
+    public function get_last_wibble() {
+        return $this->lastwibble;
+    }
+
+    public function get_current_state() {
+        return $this->currentstate;
+    }
+
+    public function get_direction() {
+        return $this->direction;
+    }
+
+    public function set_current_state($state) {
+        $this->currentstate = $state;
+    }
+
+    public function set_direction($direction) {
+        $this->direction = $direction;
+    }
+}