Testing your solution before publishing it is crucial as it will help you detect any issues and rectify it at the earliest. Vertical Solutions allows you to test your solution in a sandbox environment. This will help you to verify if all the customization, automation and other changes are working the way you expect it to. For example, you can check if an automation rule is getting executed properly by actually triggering it from the end user instance. For instance, you have an automation rule created to send an email to every new lead added to solution. You can test if this rule is getting executed properly by creating a lead in the sandbox environment.  

A sandbox is a testing environment that is used to test your code by creating a virtual space where you can work on the end user instance of your solution. The main advantage of the sandbox environment is that it isolates the end user instance of your solution from your developer console. Hence any changes made via sandbox will not get reflected in your actual solution.

To test your solution in a sandbox environment