Release testing instructions for WC Payments 5.3.0

Store order ID to session, check it before update/create_confirm intents PR #5247

This PR primary aim is to prevent creating duplicate orders.

Add this snippet to your site https://gist.github.com/htdat/8971b603ea0ab4fe07474a7a7b30000c. You can add it with plugin Code Snippets or directly to the bottom of file woocommerce-payments.php in the plugin file. Remember to remove the first line <?php; otherwise, it can create a fatal error. This snippet has two purposes:
- (1) Stimulate errors that customers can face when trying to check out an order.
- (2) Display the current session value for wcpay_processing_order at http://test-site.url/?dump_session
Log into an existing account.
When you're asked to make a payment, please randomly choose between two testing cards: 4242424242424242 (basic) and 4000002760003184 (3DS).

Please test 4 scenarios:

Add some products to the cart, visit to the checkout page.
Open a new tab, visit http://test-site.url/?dump_session. Confirm that Nothing stored.
Make a payment in the checkout page.
See an error due to our snippet
- For non-UPE flow: See an error in the checkout page.
- For UPE flow: see that the maybe_process_upe_redirect process was interrupted.
Visit this tab again http://test-site.url/?dump_session - it should display the progressing order_id, e.g. xyz.
Open another tab, check in WP Admin -> Orders, this progressing order_id xyz is precisely the newest order. After a while, this order xyz should be changed to Processing/Paid.
Go back to the checkout tab, attempt to make another payment.
Get redirected to order-received page of order xyz with this parameter wcpay_paid_for_previous_order=yes, which includes a blue notice message, something like this screenshot.
Check this order xyz in WP Admin, see a note like this: WooCommerce Payments: detected and deleted order ID abc, which has duplicate cart content with this order.. Order ID abc is different from xyz and usually bigger than xyz.
Visit http://test-site.url/?dump_session - confirm that Nothing stored.

Remove or deactivate the snippet added in the Setup step.

Add this snippet to your site https://gist.github.com/htdat/6a52eec1be77b8442ac05401908a3627 (Note: this one is slighly different from the snippet in PR 5247). You can add it with plugin Code Snippets or directly to the bottom of file woocommerce-payments.php in the plugin file. Remember to remove the first line <?php; otherwise, it can create a fatal error. This snippet tries to stimulate errors that customers can face when trying to check out an order.
When you're asked to make a payment, please randomly choose between two testing cards: 4242424242424242 (basic) and 4000002760003184 (3DS).

Before starting the test, please try to edit woocommerce-payments.php with this diff https://gist.github.com/htdat/09eef1ed0cbeec50a5354ca8da38d623

If that's not possible, please use only 3DS card when testing non-UPE flow.

Please test 4 scenarios:

Add some products, visit to the checkout page.
Try to make an payment in the checkout page.
See an error due to our snippet (trying to replicate potential issues that real customers can get).
See this order (usually the newest order) in WP Admin > Order, confirm that it has not been paid.
Try to make another payment again.
Get redirected to order-received page of this order with this parameter wcpay_previous_successful_intent=yes, like this screenshot.