When clicking the Validate button in the Home Tab, the rule application will be checked for any errors associated with invalid rule application elements such as rules, endpoints, etc. Any errors found will be displayed in a tool window at the bottom of the screen. In most cases, double-clicking on the error will navigate you to the offending item that caused the error to occur.
In this example, an If-Then rule was referring to a field 'Field2' which could not be found. All of these types of errors must be resolved before the rule application can be tested in irVerify.
Clicking the Test button will perform the same validation, and if no errors are found, then irVerify will be launched. See irVerify for Rule Testing