What do you understand by Test doubles?

Test Doubles: Stand-Ins for Real Objects in Testing

A test double is an object used in unit testing that substitutes for a real object. It's commonly referred to as a "mock" object. Test doubles help isolate the code under test by providing controlled behavior for its dependencies.

Types of Test Doubles:

There are several types of test doubles, each with slightly different characteristics:

Stubs: These are simple objects that return predefined values or perform predetermined actions. They typically have limited functionality and are used to simulate specific scenarios.

Mocks: Mocks are more sophisticated than stubs. They can define expectations about how they will be interacted with during the test and verify if those expectations are met. This allows for more complex testing scenarios.

Fakes: Fakes are fully functional objects that can be used independently of the system being tested. They often provide realistic behavior but may not have the same implementation details as the real object.

Dummies: Dummies are lightweight objects that simply occupy space in the code. They typically have no functionality and are used as placeholders when a real object isn't required for the test.

Thinking of Test Doubles as Movie Stunt Doubles

An analogy can be drawn between test doubles and stunt doubles in movies. Just like a stunt double stands in for the real actor during dangerous or complex scenes, a test double stands in for a real object during testing. Each type of test double serves a different purpose, similar to how different types of stunt doubles might be used for specific actions.

Key Points to Remember:

Stubs: Predefined behavior, limited functionality.

Mocks: Defined expectations, and verification.

Fakes: Independent functionality, realistic behavior (may differ from real object).

Dummies: Placeholders, no functionality.