Add CMS Static Block After Add to Cart in Magento 1.9

add this to the your class:

private $blockFactory;

and make your constructor look like this:

public function __construct(
    PageFactory $pageFactory,
    \Magento\Cms\Model\BlockFactory $blockFactory
  )
{
    $this->pageFactory = $pageFactory;
    $this->blockFactory = $blockFactory;
}

you can even remove the $pageFactory dependency if you don't need it anymore.

Then replace:

$testPage = [
    'title' => 'Test page title',
    'identifier' => 'test-page',
    'stores' => [0],
    'is_active' => 1,
    'content_heading' => 'Test page heading',
    'content' => 'Test page content',
    'page_layout' => '1column'
];

$this->pageFactory->create()->setData($testPage)->save();

with

$testBlock = [
    'title' => 'Test block title',
    'identifier' => 'test-block',
    'stores' => [0],
    'is_active' => 1,
];
$this->blockFactory->create()->setData($testBlock)->save();

You are using Mage class, which has been removed in Magento 2. The Magento 2 equivalent of

<?php echo Mage::helper('checkout/cart')->getAddUrl($product) ?>

is as below:

Method 1

<?php echo $objectManager->get('Magento\Checkout\Helper\Cart')->getAddUrl($product) ?>

Method 2:

Also, Note that you should avoid using Object Manager in Magento 2. It is not a good practice. So, to avoid using Object Manager you have to write following in your template's Block File:

protected $_cartHelper;

public function __construct(
   \Magento\Checkout\Helper\Cart $cartHelper
) {
   $this->_cartHelper = $cartHelper;
}

public function getAddToCartUrl($product, $additional = []) {
   return $this->_cartHelper->getAddUrl($product, $additional);
}

For method 2, you can use Magento\Catalog\Block\Product\View class's getAddToCartUrl function as your reference.