public function testRecursion()
 {
     $block1 = new DxfBlock();
     $block2 = new DxfBlock();
     $block3 = new DxfBlock();
     $block4 = new DxfBlock();
     $block1->add(10, 11);
     $block1->add(4, "fff");
     $block2->add(90, 9);
     $block2->addBlock($block1);
     $block3->addBlock($block1);
     $block3->addBlock($block2);
     $block4->add(5, "hello");
     $block4->addBlock($block3);
     $block4->addBlock($block2);
     $block4->add(1, 1);
     $block4->addBlock($block1);
     $stringExpected = "5\r\nhello\r\n10\r\n11\r\n4\r\nfff\r\n90\r\n9\r\n10\r\n11\r\n" . "4\r\nfff\r\n90\r\n9\r\n10\r\n11\r\n4\r\nfff\r\n1\r\n1\r\n10\r\n11\r\n" . "4\r\nfff\r\n";
     $this->assertEquals($stringExpected, $block4->toString());
 }