<?php

use Laminas\Stdlib\ArrayUtils;
use PHPUnit\Framework\TestCase;

/**
 * The class to test
 */
class Foo
{
    public function mergeAndFoo(array $array1, array $array2)
    {
        $merged = ArrayUtils::merge($array1, $array2);
        $merged[] = 'foo';
        
        return $merged;
    }
}

class Static2Test extends TestCase
{
    public function testMergeAndFoo() : void
    {
        $mock = Mockery::mock('alias:' . ArrayUtils::CLASS);
        $mock->shouldReceive('merge')
            ->andReturn([]);
        
        $array1 = ['bar', 'baz'];
        $array2 = [100, 200];
        
        $foo = new Foo();
        $actual = $foo->mergeAndFoo($array1, $array2);
        
        $this->assertEquals(['foo'], $actual);
    }
    
    protected function tearDown() : void
    {
        Mockery::close();
    }
}

Time: 00:00.008, Memory: 18.00 MB

OK (1 test, 0 assertions)

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PHP 8.3, Laminas MVC 3.2, Symfony 5.2, Laravel 8.28, PHPUnit 9.5, Doctrine ORM 2.8