What is Regression Testing?

If a piece of Software is modified for any reason testing needs to be done to ensure that it works as specified and that it has not negatively impacted any functionality that it offered previously. This is known as Regression Testing.

Regression Testing attempts to verify:

- That the application works as specified even after the changes/additions/modification were made to it

- The original functionality continues to work as specified even after changes/additions/modification to the software application

- The changes/additions/modification to the software application have not introduced any new bugs

When is Regression Testing necessary?

Regression Testing plays an important role in any Scenario where a change has been made to a previously tested software code. Regression Testing is hence an important aspect in various Software Methodologies where software changes enhancements occur frequently.

Any Software Development Project is invariably faced with requests for changing Design, code, features or all of them.

Some Development Methodologies embrace change.

For example 쁄xtreme Programming Methodology advocates applying small incremental changes to the system based on the end user feedback.

Each change implies more Regression Testing needs to be done to ensure that the System meets the Project Goals.

Why is Regression Testing important?

Any Software change can cause existing functionality to break.
Changes to a Software component could impact dependent Components.

It is commonly observed that a Software fix could cause other bugs.

All this affects the quality and reliability of the system. Hence Regression Testing, since it aims to verify all this, is very important.

Making Regression Testing Cost Effective:

Every time a change occurs one or more of the following scenarios may occur:
- More Functionality may be added to the system
- More complexity may be added to the system
- New bugs may be introduced
- New vulnerabilities may be introduced in the system
- System may tend to become more and more fragile with each change

After the change the new functionality may have to be tested along with all the original functionality.

With each change Regression Testing could become more and more costly.

To make the Regression Testing Cost Effective and yet ensure good coverage one or more of the following techniques may be applied:

- Test Automation: If the Test cases are automated the test cases may be executed using scripts after each change is introduced in the system. The execution of test cases in this way helps eliminate oversight, human errors,. It may also result in faster and cheaper execution of Test cases. However there is cost involved in building the scripts.

- Selective Testing: Some Teams choose execute the test cases selectively. They do not execute all the Test Cases during the Regression Testing. They test only what they decide is relevant. This helps reduce the Testing Time and Effort.

Regression Testing What to Test?

Since Regression Testing tends to verify the software application after a change has been made everything that may be impacted by the change should be tested during Regression Testing. Generally the following areas are covered during Regression Testing:

- Any functionality that was addressed by the change

- Original Functionality of the system

- Performance of the System after the change was introduced

Regression Testing How to Test?

Like any other Testing Regression Testing Needs proper planning.
For an Effective Regression Testing to be done the following ingredients are necessary:

- Create a Regression Test Plan: Test Plan identified Focus Areas, Strategy, Test Entry and Exit Criteria. It can also outline Testing Prerequisites, Responsibilities, etc.

- Create Test Cases: Test Cases that cover all the necessary areas are important. They describe what to Test, Steps needed to test, Inputs and Expected Outputs. Test Cases used for Regression Testing should specifically cover the functionality addressed by the change and all components affected by the change. The Regression Test case may also include the testing of the performance of the components and the application after the change(s) were done.

- Defect Tracking: As in all other Testing Levels and Types It is important that Defects are tracked systematically, otherwise it undermines the Testing Effort. 

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