Let us get on with a simple example – Consider a piece of JAVA code having 1000+ lines. First of all, this violates SRP (Single responsibility principle), which states that a code module should only take care of one functionality. It is like the divide and conquers principle applied in software development.

Anyways, violating principles or not, you have this code now. How do you plan to perform Unit testing? It becomes complex to unit test this extended code and ensure proper coverage. No coming to the definition of Unit testing –

Unit testing is a software development process where units of software, application, or code units are tested independently to ensure proper working and desired results. In Unit testing, codes and functionalities are isolated to ensure accurate operations.

Unit testing also favors quick testing of new changes or methods to the existing code. Manual Unit testing is done by developers at the early stages of the project and also saves a lot of time and effort in the later stages.

Unit testing, an essential component of Test-Driven development, has three stages –

Plan: Preparation of unit test and review.

Design: Test cases and scripts are made.

Test: Code is unit tested.

One of the most popular frameworks for Unit testing is JUnit. In JUnit, you can use Mock Objects and initialize objects with the new keyword. You also don’t need to worry about in-container resources, JDBC connection pools, JNDI, etc. The mock Object testing technique makes it easy to perform isolated unit tests.

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