To efficiently generate the required data for each unit test, the best approach is to use @TestSetup with a void method. This annotation allows you to create common test data that is available for all test methods in the test class. The data is rolled back after each test method, so you don't have to worry about deleting or modifying it.
This way, you can avoid duplicating code and improve performance by reducing the number of DML operations. The other options are not correct because:
* Creating test data before Test.startTest in the unit test means that you have to repeat the same code for every test method that needs the same data. This can make your test class longer and harder to maintain.
It also consumes more DML statements and governor limits.
* Creating a mock using the Stub API is useful for testing callouts or interfaces, not for creating test data.
A mock object is a fake object that simulates the behavior of a real object. It does not persist any data in the database.
* Adding @IsTest(seeAllData=true) at the start of the unit test class is not a good practice, as it makes your test methods depend on the data in the org. This can cause your tests to fail or behave inconsistently if the data changes or is not available. It also exposes your test methods to the risk of violating data privacy or security policies. References:
* Generate Data for Tests
* Testing Best Practices
* Free Salesforce Platform Developer 1 Practice Exam (With Answers)