JMock
JMock is a Java library for creating mock objects in unit tests, allowing developers to simulate dependencies and verify interactions in a test-driven development (TDD) environment. It uses a fluent API to define expectations and constraints on how mock objects should behave during tests, helping isolate the code under test from external systems.
Developers should learn JMock when writing unit tests for Java applications that have complex dependencies, such as database connections or external APIs, to ensure tests are fast, reliable, and focused on specific logic. It is particularly useful in TDD workflows to design interfaces and validate interactions without relying on real implementations, reducing test flakiness and improving code quality.