Can I test my changes in a sandbox before deploying them to production?

Of course you can. Salesforce allows you to create a sandbox containing a full copy of your production environment including Financials: 

  1. Log on to your Salesforce org.

  2. Select Setup.

  3. In Quick Find, enter Sandboxes.

  4. Select Sandboxes.

  5. Select New Sandbox, and then use the full license to create a complete copy of your production environment.

For more information, see Deploy Enhancements from Sandboxes in Salesforce Help.