What is the difference between Smoke, Sanity, and Regression testing?

Smoke testing is a basic check to ensure that the main functions of the application work and that the build is stable for further testing. It is usually a quick set of tests run after the build.

Sanity testing is a more narrow set of tests aimed at verifying specific fixes or new features. The goal is to ensure that the changes work and do not break the main functionality.

Regression testing is a full or partial rerun of tests to ensure that new changes have not caused errors in the already functioning features.

In summary:

• Smoke — readiness check for testing.
• Sanity — check of specific changes.
• Regression — check for absence of side effects after changes.