PHP Performance test for isset() vs array_key_exists() vs coalesce operator

perf_test.php

<?php

$iterations = 1000000;

$arr = ['foo' => 'bar'];

function testIsset()
{
    global $iterations, $arr;

    $startTime = microtime(true);

    for ($i = 0; $i < $iterations; $i += 1) {
        $val1 = isset($arr['foo']) ? $arr['foo'] : 'baz';
        $val2 = isset($arr['boo']) ? $arr['boo'] : 'qux';
    }

    $endTime = microtime(true);
    $elapsedTime = $endTime - $startTime;

    echo "isset():            {$elapsedTime} seconds\n";
}

function testArrayKeyExists()
{
    global $iterations, $arr;

    $startTime = microtime(true);

    for ($i = 0; $i < $iterations; $i += 1) {
        $val1 = array_key_exists('foo', $arr) ? $arr['foo'] : 'baz';
        $val2 = array_key_exists('boo', $arr) ? $arr['boo'] : 'qux';
    }

    $endTime = microtime(true);
    $elapsedTime = $endTime - $startTime;

    echo "array_key_exists(): {$elapsedTime} seconds\n";
}

function testCoalesce()
{
    global $iterations, $arr;

    $startTime = microtime(true);

    for ($i = 0; $i < $iterations; $i += 1) {
        $val1 = $arr['foo'] ?? 'baz';
        $val2 = $arr['boo'] ?? 'qux';
    }

    $endTime = microtime(true);
    $elapsedTime = $endTime - $startTime;

    echo "coalesce:           {$elapsedTime} seconds\n";
}

echo "{$iterations} iterations:\n";

testIsset();
testArrayKeyExists();
testCoalesce();