Final Answer:
The developer do to ensure that the private methods can be accessed by the test class is D. Add the TestVisible attribute to the Apex methods.
Step-by-step explanation:
To ensure that private methods in an Apex class can be accessed by the test class, the developer should add the TestVisible attribute to the Apex methods. This attribute allows the methods to be visible to test classes without making them public or global.
Adding the TestVisible attribute specifically to the methods in the Apex class is the correct approach. This attribute grants visibility to the methods only during testing, maintaining their encapsulation in other contexts. It's a targeted solution, ensuring that the necessary methods are accessible for testing purposes without compromising the overall design of the class.
Private methods in Apex classes are encapsulated and not directly visible to test classes by default. However, the TestVisible attribute allows selective visibility for testing purposes. By adding TestVisible to the specific methods needing testing access, developers strike a balance between maintaining encapsulation and facilitating effective unit testing.
This approach enhances the security of the codebase outside of testing scenarios while providing the necessary flexibility for comprehensive testing. It's a best practice to limit visibility only where required, and the TestVisible attribute aligns with this principle.
Therefore, the correct answer is: D. Add the TestVisible attribute to the Apex methods.