Why@TestSetup?
The@TestSetupannotation creates a baseline set of test data once per test class.
Test methods reuse this data, avoiding the need to recreate it repeatedly, which improves efficiency.
Why Not Other Options?
A: HttpCalloutMock is used for mocking callouts, not for creating test data.
C: UsingseeAllData=trueis discouraged because it relies on org data, violating test isolation principles.
D: While creating data inTest.startTest()works, it is less efficient than@TestSetupfor shared data.
References:Test Setup Methods:https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode
/apex_testing_testsetup.htm