Mocks

In testing, a mock is a simulated object that mimics the behavior of a real object used in production- we use mock in cases where we need to test something that requires a feature that is not yet available, so we simulate it. 

Mocks are used to isolate the code under test from its dependencies, such as databases, APIs, or other classes. 

By using mocks, you can control the inputs to the code being tested and verify how it interacts with its dependencies. This makes tests more reliable and easier to write. 

For example, if you're testing a function that interacts with a database, you could use a mock database object to simulate the database's behavior without actually connecting to a real database. 

Mock objects are lookalikes that replace external systems to help maintain testability. For example, instead of pulling live weather data, a mocked service can return predefined temperatures, allowing testers to verify the display without relying on the real service.

Mocks can be difficult to build and maintain, especially when the external service evolves. However, they are useful when components are slow, unavailable, indeterministic, under development, or require rare responses. 

Test setups vary based on the number of mocks used: 

Mocks can be implemented via MockServer, Mockoon, Mocki, or frameworks like JMock and Mockito. Dependency Injection helps swap components efficiently. Some systems allow modifying components to serve as their own mock or using control interfaces and test-specific triggers (e.g., a test user named "CrashAtStepX").