A developer implements a Queueable class that makes an external REST callout. The developer needs to test this class using Test.startTest() and Test.stopTest(). What is required for the callout to succeed in the test method?
Platform asynchronous execution, including Queueable jobs, prohibits live outbound HTTP requests during tests to prevent unpredictable external dependencies. To satisfy the requirement for making an external REST callout within a test method, implementing the `HttpCalloutMock` interface and registering it via `Test.setMock()` intercepts the runtime request and supplies a pre-configured fake response. This mechanism bypasses the platform's execution block, allowing the callout logic to complete successfully when `Test.stopTest()` synchronously flushes the asynchronous queue.
Why this answer
Callouts are not allowed in test methods unless mocked. The test must implement the HttpCalloutMock interface to simulate the response.