MDL-39725 database: Include stats collections in unit tests

lib/ddl/tests/ddl_test.php

@@ -1545,6 +1545,9 @@ class core_ddl_testcase extends database_driver_testcase {
         $this->assertSame($records[1]->secondname, $this->records['test_table1'][0]->secondname);
         $this->assertSame($records[2]->intro, $this->records['test_table1'][1]->intro);
 
+        // Collect statistics about the data in the temp table.
+        $DB->update_temp_table_stats();
+
         // Drop table1.
         $dbman->drop_table($table1);
         $this->assertFalse($dbman->table_exists('test_table1'));
@@ -1558,6 +1561,9 @@ class core_ddl_testcase extends database_driver_testcase {
             $this->assertInstanceOf('ddl_table_missing_exception', $e);
         }
 
+        // Collect statistics about the data in the temp table with less tables.
+        $DB->update_temp_table_stats();
+
         // Fill/modify/delete a few table0 records.
 
         // Drop table0.