picking-test-doubles

Prefer fakes for state-bearing dependencies to validate behavior without coupling to implementation details; use mocks only when you must verify specific interactions, such as confirming a method was called with expected parameters.

Use Robolectric shadows to substitute Android framework behavior in unit tests, such as controlling time progression via ShadowSystemClock, when you need realistic framework substitution without a physical device.

In-memory fakes are the best test double for verifying repository logic in Kotlin, as they validate state transitions and data handling without coupling your tests to internal implementation details.

You can use spies to verify method interactions, but spies are discouraged unless refactoring your code to use mocks is impractical, as they tightly couple tests to implementation behavior.

Swap Hilt bindings by mapping your testing intent to a specific test double like a fake or mock, replacing the production dependency in your Hilt testing modules to isolate components during integration tests.

A dummy test double is used as a placeholder in Kotlin testing when a dependency parameter is required for method signatures but is never actually invoked or verified during the specific test scenario.