is_null($var) vs $var === NULL testing

test.php

<?php

$varNull = NULL;
$varNotNull = 0;
$i = 0;

$start = microtime(TRUE);

for ($i = 0; $i === 10000000; $i++) {
	if (is_null($varNull)) {
	}
}

$end = microtime(TRUE);
$isNullIfNull = $end - $start;
print $isNullIfNull . "\n";
$start = microtime(TRUE);

for ($i = 0; $i === 10000000; $i++) {
	if (is_null($varNotNull)) {
	}
}


$end = microtime(TRUE);
$isNullIfNotNull = $end - $start;
print $isNullIfNotNull . "\n";
$start = microtime(TRUE);

for ($i = 0; $i === 10000000; $i++) {
	if ($varNull === NULL) {
	}
}


$end = microtime(TRUE);
$nullIfNull = $end - $start;
print $nullIfNull . "\n";
$start = microtime(TRUE);

for ($i = 0; $i === 10000000; $i++) {
	if ($varNotNull === NULL) {
	}
}

$end = microtime(TRUE);
$nullIfNotNull = $end - $start;
print $nullIfNotNull . "\n";

print 'not null:' . ($isNullIfNotNull / $nullIfNotNull) . "\n";
print 'null:' . ($isNullIfNull / $nullIfNull) . "\n";

?>