diff -u b/core/modules/system/lib/Drupal/system/Tests/Common/BreakpointsTest.php b/core/modules/system/lib/Drupal/system/Tests/Common/BreakpointsTest.php
--- b/core/modules/system/lib/Drupal/system/Tests/Common/BreakpointsTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Common/BreakpointsTest.php
@@ -29,7 +29,8 @@
       'mobile' => '(min-width: 0em)',
       'wide' => 'screen and (min-width: 40em)',
     );
-    config_install_default_config('theme', 'seven');
+    // theme_enable is needed so config gets loaded.
+    theme_enable(array('seven'));
     $this->assertEqual(system_breakpoint_list('seven'), $expected);
   }
 }