There's no need to create a separate test account with TaxCloud. Every account is in test mode until a website's API credentials associated with the account goes live (by pressing a "Go Live" button in TaxCloud).
You can associate as many websites with your TaxCloud account as you want, and each will be given a unique set of API credentials. All transactions from a Website's API credentials are test transactions until you specifically press the Go Live button for that particular Website. Once a Website is marked as Live in TaxCloud, all transactions from that point forward will be included in our automatically generated (and optionally filed) sales tax returns and reports.
All of your development and staging websites that are not marked as Live will behave exactly like your Live production websites, but those transactions will never be included in any sales tax returns or reports.