Update testing instructions for 5.9.0 to include screenshots and smoke test

Author: opr

docs/testing/releases/590.md

@@ -13,6 +13,37 @@ Zip file for testing: [woocommerce-gutenberg-products-block.zip](https://github.
 5. Add the _All Products_ & _Products by Category_ blocks to the 2/3 column
 6. Check the font sizes of the elements in the editor
 7. Check the font sizes of the elements in the frontend
+8. Ensure the page is displaying correctly.
+
+<table>
+<tr>
+<td>Editor before:
+<br><br>
+
+![#2630-editor-before](https://user-images.githubusercontent.com/3323310/128177253-29760c2e-05df-4f65-800d-071bc33534f5.png)
+</td>
+<td>Editor after:
+<br><br>
+
+![#2630-editor-after](https://user-images.githubusercontent.com/3323310/128177189-2c749dcb-dae8-429b-8f81-20da3ec6b1b1.png)
+</td>
+</tr>
+</table>
+
+<table>
+<tr>
+<td>Frontend before:
+<br><br>
+
+![#2630-frontend-before](https://user-images.githubusercontent.com/3323310/128176355-e2680e23-1d30-4f7b-8ca9-35e04119cdf5.png)
+</td>
+<td>Frontend after:
+<br><br>
+
+![#2630-frontend-after](https://user-images.githubusercontent.com/3323310/128176352-884eff43-ec7c-4c38-9d79-618528635173.png)
+</td>
+</tr>
+</table>
 
 ### Add extensibility point for extensions to filter payment methods ([4668](https://github.com/woocommerce/woocommerce-gutenberg-products-block/pull/4668))
 
@@ -32,3 +63,14 @@ registerPaymentMethodExtensionCallbacks( 'woocommerce-marketplace-extension',
 3. Go to the Checkout block
 4. Notice that Cash on delivery is no longer available
 5. Notice that Check payments are available only when the Country is Germany and the Postcode for Billing data is 12345
+
+### Smoke test the Checkout block
+Because of experimental work done during this release, we need to ensure no regressions have been made to the checkout block. Please smoke test the checkout block.
+
+1. Enable a few different payment methods in your store.
+2. Add some products to your cart. 
+3. Go to the Checkout block, ensure it displays with no errors and the correct cart contents are showing.
+4. Ensure you can enter your shipping and billing addresses.
+5. Ensure validation still works, (focus a field, delete the content and ensure an error is shown, e.g. postcode field).
+6. Ensure you can use different payment methods.
+7. Ensure you can check out and that the order is placed.