private function _warmup()
    {
        $warmup = new Test('warmup', function () {
        });

        $this->_overhead = $warmup->runTest($this->_count);

        // One call each method for init (warmup)

        /** @var Test $test */
        foreach ($this->_tests as $test) {
            $test->runTest(1);
        }

        $this->out(
            'PHP Overhead: ' .
            'time=' . Timer::formatMS($this->_overhead['time']) . '; ' .
            'memory=' . FS::format($this->_overhead['memory'], 2) . ';' .
            PHP_EOL
        );
    }