Exam AD0-E103 topic 1 question 62 discussion

A banking AEM application contains functionality to calculate a mortgage rate based on user input. A servlet in place calculates the result in the backend. A call to an internal third-party REST service is required to retrieve the average object value based on a given zip code.
The following three service interfaces are used:
MortgageCalculationServlet, MortgageCalculationService and ObjectValueLookupRestService where MortgageCalculationServlet has a dependency to MortgageCalculationService and MortgageCalculationService has a dependency to ObjectValueLookupRestService.
The calculation has many combinations of input parameters and edge cases, so the JUnit coverage must be as high as possible.
Which two strategies should the developer use to ensure testability of the application code? (Choose two.)