DboSource::lastError PHP Method

    public function lastError(PDOStatement $query = null)
    {
        if ($query) {
            $error = $query->errorInfo();
        } else {
            $error = $this->_connection->errorInfo();
        }
        if (empty($error[2])) {
            return null;
        }
        return $error[1] . ': ' . $error[2];
    }

 /**
  * testLastError
  *
  * @return void
  * @access public
  */
 function testLastError()
 {
     $debug = Configure::read('debug');
     Configure::write('debug', 0);
     $this->db->simulate = false;
     $query = 'SELECT [name] FROM [categories]';
     $this->assertTrue($this->db->execute($query) !== false);
     $this->assertNull($this->db->lastError());
     $query = 'SELECT [inexistent_field] FROM [categories]';
     $this->assertFalse($this->db->execute($query));
     $this->assertNotNull($this->db->lastError());
     $query = 'SELECT [name] FROM [categories]';
     $this->assertTrue($this->db->execute($query) !== false);
     $this->assertNull($this->db->lastError());
     Configure::write('debug', $debug);
 }