What is the purpose of a "stub" in software testing?

Answer: To simulate the behavior of a missing or incomplete module

Explanation: Stubs are simple, temporary implementations used in testing to stand in for dependent modules that are not yet developed or are unavailable. They provide fixed or pre-defined responses so the module under test can be exercised in isolation.

• Allow early testing: Enable testing of a component before its dependencies are ready.

• Isolate behavior: Help isolate the logic of the module under test by removing variability from dependencies.

• Simplify setup: Reduce complexity of test environments by replacing external services with lightweight substitutes.

Contrast with mocks: Mocks often include verification of interactions and expectations, whereas stubs typically only provide canned responses without asserting how they were called.

Example: If a payment service is not available during testing, use a stub that returns a successful payment response for certain inputs so you can test order processing logic without the real payment system.