If it's solely the data and the specific assignments that you need, these options are the most agile:
Create/record a unittest for the Case Type which records all data and transitions up until the point that you require.
Use the PegaAPI to create, update and transition your case to the desired stage.
The first option requires only Pega and is the quickest way. The latter one requires an external application to execute the REST calls and requires a bit more work. The alternative approach is to use a test automation tool, like Selenium or Tosca, and is more labor intensive.
You can use PegaUnit testing to create test cases for your applications. After you develop rules, you can test them, and then convert the test runs to PegaUnit test cases to validate application data by comparing expected property values with the actual values returned by running the rule. You can create PegaUnit test cases for a number of rule types, including case types and flows.