Optimize regression testing

Regression testing refers to testing a previously tested program, after a modification. It ensures that defects have not been introduced or discovered in unmodified parts of the software, as a result of the modifications made.
These tests are performed when the software or its environment is modified. The objective of a regression campaign is to check whether the changes made to the software (or to its environment) have not caused major bugs in the functionality already in place. And therefore whether these changes have caused major regressions.
This definition highlights important principles such as software testing that has already been tested before or the subsequent modification of the same software. A regression test rarely stands alone. It is part of a coherent set of several tests, each with its own characteristics and objectives. 

The frequency of regression testing will depend on the specific software application and the nature of the changes being made. It is generally recommended to perform regression testing after any significant changes have been made to the software, as well as regularly during the development process to catch any issues early on.
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Yes, regression testing can be automated using tools and scripts. Automating regression testing can help to save time and resources, as well as ensure that tests are consistently performed in the same way.

Any significant changes to a software application, such as new features or modifications to existing functionality, should be subject to regression testing. It is also important to perform regression testing when integrating new modules or components into the software.