DI Scenario 1

<?php

interface GameInterface
{
    public function checkLevel();
}

class Game
{
    public $game;

    public function __construct(GameInterface $game)
    {
        $this->game = $game;
    }

    public function play()
    {
        $className = get_class($this->game);

        if ($this->game->checkLevel() === true) {
            return "{$className} can play";
        }

        return "{$className} can't play";
    }
}

class Mario implements GameInterface
{
    public function checkLevel()
    {
        return true;
    }
}

class Race implements GameInterface
{
    public function checkLevel()
    {
        return false;
    }
}

echo (new Game(new Mario))->play() . PHP_EOL;
echo (new Game(new Race))->play() . PHP_EOL;