public function testExists()
{
$elements = [1, 'A' => 'a', 2, 'null' => null, 3, 'A2' => 'a', 'zero' => 0];
$collection = new ArrayCollection($elements);
$this->assertTrue($collection->exists(function ($key, $element) {
return $key === 'A' && $element === 'a';
}), 'Element exists');
$this->assertFalse($collection->exists(function ($key, $element) {
return $key === 'non-existent' && $element === 'non-existent';
}), 'Element not exists');
}