Difference between regression, sanity and smoke tests

Regression testing is a type of software testing conducted after a code update to ensure that the update introduced no new bugs. This is because new code may bring in new logic that conflicts with the existing code, leading to defects. Usually, QA teams have a series of regression test cases for important features that they will re-execute each time these code changes occur to save time and maximize test efficiency. 

Smoke testing is a software testing technique performed post software build to verify that the critical functionalities of software are working fine. It is executed before any detailed functional or regression tests are executed. The main purpose of smoke testing is to reject a software application with defects so that QA team does not waste time testing broken software applications.

In smoke testing, the test cases chose to cover the most important functionality or component of the system. The objective is not to perform exhaustive testing, but to verify that the critical functionalities of the system are working fine. For Example, a typical smoke test would be –to verifythat the application launches successfully, Check that the GUI is responsive … etc.

Sanity testing is a kind of software testing performed after receiving a software build, with minor changes in code, or functionality, to ascertain that the bugs have been fixed and no further issues are introduced due to these changes. The goal is to determine that the proposed functionality works roughly as expected. If sanity test fails, the build is rejected to save the time and costs involved in a more rigorous testing.