Unit testing is the practice of testing individual components or modules of a software application. Unit tests are typically automated and executed as part of the software development process, providing rapid feedback on the functionality of individual components. Unit tests are typically focused on verifying that individual functions, methods, or classes behave as expected and produce the correct results.

Integration testing is the process of testing how different components or modules of a software application work together. Integration tests are typically executed after unit tests, and they help to identify any compatibility issues or unexpected interactions between different parts of the application. Integration tests can help to identify issues early in the development process, before they become more difficult and time-consuming to resolve.

• Testing how different modules or components work together in a software application.
• Example: Testing the integration between a database and a web-based front-end, to verify that data is correctly displayed and updated.

Acceptance testing is the final stage of testing before a software application is deployed to production. Acceptance testing is performed by end-users, stakeholders, or quality assurance teams, and it is focused on verifying that the application meets the functional requirements and specifications. Acceptance testing is an important step in the development process, as it helps to ensure that the software application meets the needs and expectations of its intended users.

• Testing the software application from an end-user's perspective, to verify that it meets the functional requirements and specifications.
• Example: Testing an e-commerce website to verify that the checkout process is working as expected and that orders are processed correctly.
  
  

Regression testing is the process of verifying that changes to a software application do not introduce new bugs or break existing functionality. Regression tests are typically automated and executed as part of the development process, providing rapid feedback on the impact of changes to the application. Regression testing helps to ensure that software applications remain reliable and functional, even as they evolve and change over time.

• Testing the software application after changes have been made, to verify that new bugs have not been introduced and that existing functionality has not been broken.
• Example: Testing a previously working feature after a software upgrade, to verify that it still works as expected.