Fake objects in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a fake object in testing?

A fake object is a simple implementation of an interface or class used in tests to simulate real behavior with minimal logic. It helps isolate the code under test by replacing complex dependencies.

intermediate

How does a fake object differ from a mock?

A fake object has working implementations but simplified, while a mock is used to verify interactions and expectations during tests.

beginner

Why use fake objects in JUnit tests?

They speed up tests by avoiding slow or complex real components, and help test code in isolation without external dependencies.

intermediate

Example of a fake object in JUnit for a payment service?

class FakePaymentService implements PaymentService { public boolean pay(double amount) { return true; } } This fake always returns success to test payment logic without real transactions.

beginner

What is a key benefit of using fake objects over real implementations in tests?

They make tests faster, more reliable, and easier to write by removing dependencies on external systems or complex logic.

What is the main purpose of a fake object in testing?

A To replace the entire application

B To simulate a real component with simple logic

C To verify method calls and interactions

D To slow down test execution

Fake objects simulate real components with minimal logic to isolate tests and improve speed.

Which of the following is true about fake objects?

A They are never used in JUnit tests

B They are used to verify interactions only

C They contain complex business logic

D They provide simplified working implementations

Fake objects provide simplified working implementations to replace real dependencies in tests.

In JUnit, why might you use a fake object instead of the real service?

A To avoid external dependencies and speed up tests

B To make tests slower

C To increase test complexity

D To test the real service behavior

Fake objects avoid external dependencies and make tests faster and more reliable.

Which is NOT a characteristic of a fake object?

A Simplified implementation

B Used for isolation in tests

C Verifies method call counts

D Replaces complex dependencies

Verifying method calls is a feature of mocks, not fake objects.

What would a fake payment service likely do in a test?

A Always return success without real processing

B Perform real transactions

C Always return failure

D Throw exceptions randomly

A fake payment service usually returns success to test payment logic without real transactions.

Explain what a fake object is and why it is useful in JUnit testing.

Think about replacing complex parts with simple versions in tests.

Describe the difference between a fake object and a mock in software testing.

One simulates behavior, the other checks calls.