SimpleHelper example

    public function testConstructor()
    {
        $engine = new ProjectTemplateEngine(new TemplateNameParser(), $this->loader);
        $this->assertEquals($this->loader, $engine->getLoader(), '__construct() takes a loader instance as its second first argument');
    }

    public function testOffsetGet()
    {
        $engine = new ProjectTemplateEngine(new TemplateNameParser(), $this->loader);
        $engine->set($helper = new \Symfony\Component\Templating\Tests\Fixtures\SimpleHelper('bar'), 'foo');
        $this->assertEquals($helper, $engine['foo'], '->offsetGet() returns the value of a helper');

        try {
            $engine['bar'];
            $this->fail('->offsetGet() throws an InvalidArgumentException if the helper is not defined');
        } catch (\Exception $e) {
            $this->assertInstanceOf(\InvalidArgumentException::class, $e, '->offsetGet() throws an InvalidArgumentException if the helper is not defined');
            $this->assertEquals('The helper "bar" is not defined.', $e->getMessage(), '->offsetGet() throws an InvalidArgumentException if the helper is not defined');
        }
    }