What is the difference between smoke testing and sanity testing?

Smoke testing and sanity testing are both types of software testing techniques used to ensure the stability and basic functionality of an application. However, there are some key differences between the two:

1. Purpose:
- Smoke Testing: The main purpose of smoke testing is to verify if the critical functionalities of the software are working as expected after a new build or release. It is performed to determine if the application is stable enough for further testing.
- Sanity Testing: The main purpose of sanity testing is to quickly evaluate whether the specific changes or fixes made in the software have resolved the reported issues or bugs. It is performed to ensure that the major functionalities are working fine after the changes.

2. Scope:
- Smoke Testing: Smoke testing covers a wide range of functionalities and features of the software to ensure that the basic and critical components are working properly.
- Sanity Testing: Sanity testing focuses on specific areas or functionalities of the software that have been modified or fixed, rather than testing the entire application.

3. Depth:
- Smoke Testing: Smoke testing is a shallow and broad level of testing that aims to identify major issues or showstopper defects. It is not an in-depth analysis of the software.
- Sanity Testing: Sanity testing is a narrower and deeper level of testing that aims to verify the specific changes or fixes made in the software. It is more focused and detailed compared to smoke testing.

4. Execution Time:
- Smoke Testing: Smoke testing is usually performed at the beginning of the testing phase, after a new build or release, to quickly identify any critical issues. It is a subset of regression testing and is executed before more comprehensive testing.
- Sanity Testing: Sanity testing is performed after the completion of smoke testing or when specific changes or fixes have been made. It is a subset of regression testing and is executed to ensure that the modified areas are functioning correctly.

In summary, smoke testing is performed to ensure the stability of the entire application, while sanity testing is performed to verify the specific changes or fixes made in the software. Smoke testing is broader and shallower, while sanity testing is narrower and deeper. Both testing techniques are essential in the software testing and quality assurance process to ensure the overall functionality and stability of the application.