Issue #2807171 by alexpott: Use the correct testing table prefix in simpletest_clean_database()

core/modules/simpletest/simpletest.module

@@ -673,13 +673,12 @@ function simpletest_clean_environment() {
  * Removes prefixed tables from the database from crashed tests.
  */
 function simpletest_clean_database() {
-  $tables = db_find_tables(Database::getConnection()->prefixTables('{simpletest}') . '%');
-  $schema = drupal_get_module_schema('simpletest');
+  $tables = db_find_tables('test%');
   $count = 0;
-  foreach (array_diff_key($tables, $schema) as $table) {
-    // Strip the prefix and skip tables without digits following "simpletest",
-    // e.g. {simpletest_test_id}.
-    if (preg_match('/simpletest\d+.*/', $table, $matches)) {
+  foreach ($tables as $table) {
+    // Only drop tables which begin wih 'test' followed by digits, for example,
+    // {test12345678node__body}.
+    if (preg_match('/^test\d+.*/', $table, $matches)) {
       db_drop_table($matches[0]);
       $count++;
     }