Mockito Spy vs Mock: Understanding and Using Spies and Mocks Effectively

Introduction to Mocking and Spying in Mockito

Overview: Explaining the concept of mocking and spying in the context of unit testing with Mockito. Purpose: How mocks and spies contribute to isolating the unit of work and ensuring test reliability.

What are Mocks in Mockito?

Definition: Mocks are dummy implementations of classes or interfaces used for testing. Usage: How to create and use mocks to simulate external dependencies. Example:

What are Spies in Mockito?

Definition: Spies are partial mocks that allow using real object behavior while still being able to stub or verify certain method calls. Usage: When to use spies to monitor real object behavior. Example:

Key Differences between Mocks and Spies

Functionality: Comparing how mocks are entirely simulated objects, while spies wrap around real objects. Behavior: Explaining how method calls are handled in mocks vs spies.

When to Use Mocks

Scenarios: Ideal use cases for mocks, such as completely isolating a class from its dependencies. Benefits: Highlighting the advantages of using mocks, like full control over object behavior.

When to Use Spies

Scenarios: Situations where spies are more appropriate, like testing complex legacy code. Cautions: Understanding the implications of using spies, such as the risk of relying on the actual object’s behavior.

Best Practices for Using Mocks and Spies

Consistency: Maintaining consistency in test cases when using mocks and spies. Avoiding Pitfalls: Tips to avoid common mistakes while using mocks and spies.


Understanding the distinction between mocks and spies in Mockito is crucial for writing effective and reliable unit tests. Choosing the right approach for a given testing scenario ensures that tests are robust, maintainable, and accurately simulate the necessary behaviors.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.