Testing a web shop and think you're done? Here are some test ideas you may or may not have covered yet (that will still not be exhaustive):

Regions

Tested across supported countries? What differences should there be? Currency? Date & time formats? Payment methods? Shipping methods? Regulations?

Languages

Tested across supported languages? Special character rendering, capitalisation & punctuation, impact on cross-browser font rendering.

Form factors

Tested with touch navigation? Tested across supported resolutions?

Payment types

Pay now versus pay later. Credit card versus bank transfer.

User states

Check out as logged in user versus guest user. With and without address set on account. With old and new account (keep old accounts around).

Product types

Simple products. Configurable products. Bundles.

User actions

Printing a page. Letting a page time out. Navigating in landscape mode.

Product states

Out of stock product. Product with limited stock. Reserved product.

Cookie acceptance

Test impact of rejected or accepted state on cookies loaded. Choice remembered when it should be?

Cart

Other products in cart from old session. Other products in cart without stock. Other products in cart from different warehouse(s).

Microsites

Changes on main site also made on other sites when consistency is expected?

Tracking

Impact of changes on whether user data is still tracked as it should be.

Compliance

What safe shopping or other regulations need to still be safeguarded?

Performance

Impact of changes on page load time, Lighthouse score, transaction times of affected functionality.

Security

Do changes have implications for data privacy or create security vulnerabilities?

Accessibility

Do changes violate your supported level of the Web Content Accessibility Guidelines?

SEO

Verify that the structured data has the expected properties and values.