Function to find the maximum value in a nested set of arrays

App\Entity\MyMax.php

<?php

namespace App\Entity;

class MyMax
{
    public function find(array $input) {
        $max = null;

        foreach ($input as $value) {
            $result = null;
            if (is_array($value)) {
                $result = $this->find($value);
            }
            if (is_numeric($value)) {
                $result = $value;
            }
            $max = ($result > $max) ? $result : $max;
        }

        return $max;
    }
}

App\Tests\MyMaxTest.php

<?php

namespace App\Tests;

use App\Entity\MyMax;
use PHPUnit\Framework\TestCase;

class MyMaxTest extends TestCase
{
    public function testPlainArray()
    {
        $finder = new MyMax();

        $this->assertNull($finder->find([]));
        $this->assertEquals(1, $finder->find([1]));
        $this->assertEquals(2, $finder->find([1, 2]));
        $this->assertEquals(3, $finder->find([1, 1 + 2]));
    }

    public function testNestedArray()
    {
        $finder = new MyMax();

        $this->assertNull($finder->find([[]]));
        $this->assertEquals(2, $finder->find([1, [1, 2]]));
        $this->assertEquals(3, $finder->find([3, [1, 2]]));
        $this->assertEquals(3, $finder->find([3, [1, 2], [2, 3]]));
        $this->assertEquals(4, $finder->find([3, [1, 2], [4, 3]]));
        $this->assertEquals(5, $finder->find([3, [1, 2, [4, 5]], [4, 3]]));
        $this->assertEquals(1000, $finder->find([1, 2, [3, [1000, 4, 5], 6, 7], 8, 9]));
        $this->assertEquals(1000, $finder->find([1, 2, [3, [1000, 4, 5, '999'], 6, 7], 8, 9]));
        $this->assertEquals(1000, $finder->find([1, 2, [3, ['1000', 4, 5], 6, 7], 8, 9]));
        $this->assertEquals(1000, $finder->find([1, 2, [3, ['key' => 1000, 4, 5], 6, 7], 8, 9]));
        $this->assertEquals(1000, $finder->find([1, 2, [3, ['key' => '1000', 4, 5], 6, 7], 8, 9]));
        $this->assertEquals(1000, $finder->find([1, 2, [3, [1000, 4, 5, new \stdClass()], 6, 7], 8, 9]));
    }

    public function testFloat()
    {
        $finder = new MyMax();

        $this->assertEquals(1, $finder->find([1, 0.5]));
        $this->assertEquals(1, $finder->find([1, 0.5]));
    }

    public function testInfinity()
    {
        $finder = new MyMax();

        $this->assertEquals(INF, $finder->find([1, INF]));
        $this->assertEquals(1, $finder->find([1, -INF]));
        $this->assertEquals(1, $finder->find([1, log(0)]));
    }

    public function testNan()
    {
        $finder = new MyMax();

        $this->assertEquals(1, $finder->find([1, NAN]));
        $this->assertEquals(-1, $finder->find([-1, NAN]));
    }

    public function testNull()
    {
        $finder = new MyMax();

        $this->assertNull($finder->find([null]));
        $this->assertEquals(1, $finder->find([1, null]));
        $this->assertEquals(-1, $finder->find([-1, null]));
    }

    public function testNegative()
    {
        $finder = new MyMax();

        $this->assertEquals(-1, $finder->find([-1, -2]));
        $this->assertEquals(-1, $finder->find(['-1', -2]));
    }

    public function testString()
    {
        $finder = new MyMax();

        $this->assertEquals(1, $finder->find([1, 'a']));
        $this->assertEquals(1, $finder->find([1, '22a']));
        $this->assertEquals(1, $finder->find([1, 'a22']));
        $this->assertEquals(1000, $finder->find([1, 2, [3, [1000, 4, 5, 'test'], 6, 7], 8, 9]));
    }
}

my_max.php

<?php 

function my_max(array $xs) {
    $max = null;

    foreach ($xs as $value) {
        $result = null;
        if (is_array($value)) {
            $result = my_max($value);
        }
        if (is_numeric($value)) {
            $result = $value;
        }
        $max = ($result > $max) ? $result : $max;
    }

    return $max;
}

echo my_max([1, 2, [3, [1000, 4, 5], 6, 7], 8, 9]) . "\n"; // 1000