Test Cards: https://docs.adyen.com/developers/test-cards/test-card-numbers
UPDATE: Google Pay now supports dynamically showing the total price on the payments sheet. This price can also be updated as the user changes their selection at checkout (eg.: shipping option). You can configure these pricing updates as shown in the docs.
You can also check out the official announcement for more details.
Hope it helps.
TEST
environment, the APIs are, by default, still expecting valid card numbers. As such, if you use invalid information, the checks will still fail. Said so, your card is never charged nor the token that the systems responds with allows to perform any transaction.