NetSuite provides their current customers with the option to purchase a SANDBOX account which essentially is a copy of their current company production database on a separate server. Once you purchase this option from NetSuite, you can access it by selecting:
Once you purchase the sandbox account from NetSuite, the administrator of the production system has to request a REFRESH of the sandbox account, which essentially creates a copy of the production database at that time. This process typically takes about 1-2 business days. During the refresh request, you can select to only allow ADMINISTRATORS access to the sandbox account or allow all users to access the sandbox. Any workflows which trigger an e-mail notification to recipients will be prefixed with the [SANDBOX] disclaimer, allowing all parties to quickly differentiate notifications from the production account.
As with most things from NetSuite, the sandbox account is not cheap, but if you do any amount of customization in your system, usually well worth it.