mockable

Mockable refers to a component, interface, or API that can be substituted with a mock object during testing. A mock is a test double that simulates the behavior of real components, allowing tests to verify interactions and control outcomes without relying on the actual implementation.

Achieving mockability typically involves introducing abstractions such as interfaces or well-defined contracts and applying dependency inversion. Dependencies are injected rather than created internally. This enables tests to supply mock implementations that record calls and return predefined results, making the unit under test easier to isolate.

Mockability is central to unit testing, enabling isolation of a unit under test; it also supports integration testing by simulating external systems when real connections are impractical. It facilitates deterministic test results and faster feedback loops, since dependencies can be controlled and do not rely on external resources.

Benefits include deterministic tests, faster test suites, easier fault injection, and clearer contracts between components. However, there are challenges. Overuse of mocks can lead to brittle tests that tightly couple tests to implementation details. Maintaining mocks can be burdensome when interfaces evolve, and some code is inherently difficult to mock. Mismatches between mock behavior and real system behavior can create a false sense of correctness.

Related concepts include test doubles, stubs, fakes, and spies, as well as various mocking frameworks. Best practices emphasize testing observable behavior rather than specific implementations, keeping mocks minimal and aligned with actual interfaces to preserve test validity over time.