diff --git a/lib/phpunit/classes/advanced_testcase.php b/lib/phpunit/classes/advanced_testcase.php
index 6995ba7d3ce..d37a849a9f2 100644
--- a/lib/phpunit/classes/advanced_testcase.php
+++ b/lib/phpunit/classes/advanced_testcase.php
@@ -485,6 +485,9 @@ abstract class advanced_testcase extends PHPUnit_Framework_TestCase {
         unset($user->access);
         unset($user->preference);
 
+        // Enusre session is empty, as it may contain caches and user specific info.
+        \core\session\manager::init_empty_session();
+
         \core\session\manager::set_user($user);
     }
 
diff --git a/lib/phpunit/tests/advanced_test.php b/lib/phpunit/tests/advanced_test.php
index cc2d8e8b5c4..cf00787a6ab 100644
--- a/lib/phpunit/tests/advanced_test.php
+++ b/lib/phpunit/tests/advanced_test.php
@@ -72,7 +72,9 @@ class core_phpunit_advanced_testcase extends advanced_testcase {
     }
 
     public function test_set_user() {
-        global $USER, $DB;
+        global $USER, $DB, $SESSION;
+
+        $this->resetAfterTest();
 
         $this->assertEquals(0, $USER->id);
         $this->assertSame($_SESSION['USER'], $USER);
@@ -109,6 +111,11 @@ class core_phpunit_advanced_testcase extends advanced_testcase {
         $this->assertEquals(0, $USER->id);
         $this->assertSame($_SESSION['USER'], $USER);
         $this->assertSame($GLOBALS['USER'], $USER);
+
+        // Ensure session is reset after setUser, as it may contain extra info.
+        $SESSION->sometestvalue = true;
+        $this->setUser($user);
+        $this->assertObjectNotHasAttribute('sometestvalue', $SESSION);
     }
 
     public function test_set_admin_user() {