Stub objects in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a stub object in software testing?

A stub object is a simple fake version of a real object used in tests. It provides fixed responses to calls, helping isolate the part of the code being tested.

beginner

Why do we use stub objects in unit tests?

We use stubs to replace complex or slow parts of the system, like databases or web services, so tests run fast and focus only on the code under test.

intermediate

How does a stub differ from a mock object?

A stub provides preset responses but does not check how it was used. A mock also verifies if certain methods were called, adding behavior verification.

intermediate

Example of a simple stub method in JUnit?

In JUnit, a stub can be a class that implements an interface and returns fixed values. For example, a stub for a payment service might always return success.

beginner

What is a key benefit of using stub objects?

They help isolate the unit of code being tested by removing dependencies on external systems, making tests reliable and fast.

What does a stub object typically do in a test?

A Returns fixed responses to method calls

B Verifies if methods were called correctly

C Runs the full real implementation

D Generates random data for testing

A stub returns fixed responses to simulate parts of the system during testing.

Which is NOT a reason to use stub objects?

A Verify the order of method calls

B Isolate the code under test

C Avoid using real external systems

D Speed up tests by avoiding slow dependencies

Verifying method call order is a job for mocks, not stubs.

In JUnit, a stub class usually:

A Generates test reports

B Extends the test class

C Runs the real database queries

D Implements an interface with fixed return values

A stub class implements interfaces and returns fixed values to simulate behavior.

Which statement about stub objects is true?

A They check if methods were called correctly

B They replace real objects with simple versions

C They are used to test UI components

D They slow down test execution

Stubs replace real objects with simple versions to isolate tests.

What is the main difference between a stub and a mock?

A Stubs are used only in integration tests

B Mocks provide fixed responses; stubs verify interactions

C Stubs provide fixed responses; mocks verify interactions

D Mocks are slower than stubs

Stubs return fixed data; mocks also check how they were used.

Explain what a stub object is and why it is useful in unit testing.

Think about replacing parts of the system that are slow or complex.

Describe the difference between a stub and a mock object.

One just gives answers, the other checks behavior.