Unit Testing is a level of software testing where individual units/ components of a software are tested. The purpose is to validate that each unit of the software performs as designed.Unit tests are basically written and executed by software developers to make sure that code meets its design and requirements and behaves as expected.

The goal of unit testing is to segregate each part of the program and test that the individual parts are working correctly. This means that for any function or procedure when a set of inputs are given then it should return the proper values. It should handle the failures gracefully during the course of execution when any invalid input is given. A unit test provides a written contract that the piece of code must assure. Hence it has several benefits. Unit testing is basically done before integration as shown in the image below.

What is unit testing

Method Used for unit testing: White Box Testing method is used for executing the unit test.

When Unit testing should be done?

Unit testing should be done before Integration testing.

By whom unit testing should be done?

Unit testing should be done by the developers.

Advantages of Unit testing:

1. Issues are found at early stage. Since unit testing are carried out by developers where they test their individual code before the integration. Hence the issues can be found very early and can be resolved then and there without impacting the other piece of codes.

2. Unit testing helps in maintaining and changing the code. This is possible by making the codes less interdependent so that unit testing can be executed. Hence chances of impact of changes to any other code gets reduced.

3. Since the bugs are found early in unit testing hence it also helps in reducing the cost of bug fixes. Just imagine the cost of bug found during the later stages of development like during system testing or during acceptance testing.

Integration Testing:-

Integration Testing is a level of software testing where individual units are combined and tested as a group.

The purpose of this level of testing is to expose faults in the interaction between integrated units. Test drivers and test stubs are used to assist in Integration Testing.

integration testing: Testing performed to expose defects in the interfaces and in the interactions between integrated components or systems. See also component integration testing, system integration testing.

component integration testing: Testing performed to expose defects in the interfaces and interaction between integrated components.

system integration testing: Testing the integration of systems and packages; testing interfaces to external organizations (e.g. Electronic Data Interchange, Internet).

INTEGRATION METHOD:-

Any of Black Box Testing, White Box Testing, and Gray Box Testing methods can be used. Normally, the method depends on your definition of ‘unit’.

Integration Test Plan:-

Prepare

Review

Rework

Baseline