only in patch2:
unchanged:
--- a/modules/simpletest/simpletest.module
+++ b/modules/simpletest/simpletest.module
@@ -370,11 +370,25 @@ function simpletest_test_get_all() {
 
           // If this test class requires a non-existing module, skip it.
           if (!empty($info['dependencies'])) {
+
+            // Searching for an item that does not exist returns NULL.
+            // Set a custom error handler so we can ignore the file not found error.
+            set_error_handler(function($error_level, $message, $filename, $line, $context) {
+              // Skip error handling if this is a "file not found" error.
+              if (strstr($message, 'is missing from the file system:')) {
+                return;
+              }
+              _drupal_error_handler($error_level, $message, $filename, $line, $context);
+            });
+
             foreach ($info['dependencies'] as $module) {
               if (!drupal_get_filename('module', $module)) {
                 continue 2;
               }
             }
+
+            // Restore the original error handler.
+            restore_error_handler();
           }
 
           $groups[$info['group']][$class] = $info;