Differ details right below, but before that, here’s a quick definition of each terms:

• Smoke Testing: We do smoke test whenever we receive a new build that is relative unstable to ensure that the critical functionalities of the AUT working fine. The idea of this test is to find critical problems as soon as possible and reject the build so that we don’t waste time to test further (the broken build).
• Sanity Testing: We do sanity test whenever we receive a new build that is relative stable to conduct to identify the dependent missing functionalities. In other words, you will validate the major functionalities of the system in a more detailed way.

Both sanity tests and smoke tests are ways to avoid wasting time and effort by quickly determining whether an application is too flawed to merit any rigorous testing.

• Retesting: We do retesting for a feature/function which had defects (bugs) & those bugs have been fixed recently.
• Regression Testing: We do regression testing for AUT when there are changes including new features / bug fixed to make sure no impact to the current existing functionalities.

To have better understanding, let me introduce you the table of comparison as below:

Smoke Testing	Sanity Testing	Regression Testing	Re-testing
Smoke testing is executed to determine if critical functionalities of AUT are working fine	Sanity testing is executed to determine if the section of AUT is still working as design after some minor changes or bug fixes	Regression testing is executed to confirm whether a recent program or code change has not adversely affected existing features	Retesting is executed to confirm the test cases that failed in the final execution are passing after the defects are fixed
The purpose of smoke testing is to verify the "stability" of the system in order to proceed with more rigorous testing	The purpose of sanity testing is to verify the "rationality" of the system in order to proceed with more rigorous testing	The purpose of regression testing is that new changes should not have any side effects to existing functionalities	Re-testing is done on the basis of the defect fixes
Defect verification is not the part of smoke testing	Defect verification is not the part of sanity testing	Defect verification is not the part of regression testing	Defect verification is the part of re-testing
Smoke testing is executed before regression test	Sanity testing is executed before regression testing, after smoke testing	Based on the project and availability of resources, regression testing can be carried out parallel with Re-testing	- Re-testing is done before we start sanity testing - Priority of re-testing is also higher than regression testing, so it is carried out before regression testing
Smoke test can be excuted manually or automatically	Sanity test often is executed manually	You can do automation for regression testing, manual testing could be expensive and time consuming	You cannot automate the test cases for re-testing
Smoke testing is subset of Regression testing	Sanity testing is subset of Acceptance testing	Regression testing is only done when there is any modification or changes become mandatory in existing project	Re-testing executes a defect with same data and the same environment with different inputs with new build
Test cases of smoke test are part of regression testing, only cover critical functionalities	Sanity Test can be performed without test cases but domain knowledge is required	Test cases for regression testing can be obtained from the functional specification, user tutorials and manuals, and defect reports in regards to corrected problems	Test cases for re-testing can be re-used from previous executed test cases

#retesting  #regression  #smoke  #sanity  #testing