Explanation
Box 1: Unit
Unit testing is a software development process in which the smallest testable parts of an application, called units, are individually and independently scrutinized for proper operation. This testing methodology is done during the development process by the software developers and sometimes QA staff.
Box 2: Regression
What is regression testing?
Image result for Dynamics 365 what is regression testing
Regression testing is a software testing practice that ensures an application still functions as expected after any code changes, updates, or improvements. Regression testing is responsible for the overall stability and functionality of the existing features.
Box 3: Functional
FUNCTIONAL TESTING is a type of software testing that validates the software system against the functional requirements/specifications.
Box 4: End to End
End-to-end testing is a methodology that assesses the working order of a complex product in a start-to-finish process. End-to-end testing verifies that all components of a system are able to run and perform optimally under real-world scenarios.
Reference: https://www.techtarget.com/searchsoftwarequality/definition/unit-testing
https://katalon.com/resources-center/blog/regression-testing
https://www.guru99.com/functional-testing.html
https://www.techtarget.com/searchsoftwarequality/definition/End-to-end-testing