What is the difference between regression, sanity and smoke testing?

_Regression, Sanity, and Smoke Testing: Key Differences_

Regression, sanity, and smoke testing are three types of software testing techniques that serve distinct purposes. Here's a brief overview of each:

1. _Regression Testing_:

    - Purpose: Ensure that changes or fixes did not introduce new defects or affect existing functionality.

    - Scope: Test the entire application or system, focusing on areas affected by changes.

    - Depth: In-depth testing, covering various scenarios and user journeys.

    - Frequency: Performed after changes, fixes, or updates.

2. _Sanity Testing_:

    - Purpose: Verify that the application or system is working as expected, with a focus on overall functionality and user experience.

    - Scope: Test the entire application or system, covering critical functionalities.

    - Depth: High-level testing, focusing on user journeys and workflows.

    - Frequency: Performed after a build or deployment, or when time is limited.

3. _Smoke Testing_:

    - Purpose: Quickly verify that the application or system is stable and functional, focusing on critical functionalities.

    - Scope: Limited to critical functionalities and high-risk areas.

    - Depth: High-level testing, focusing on basic functionality.

    - Frequency: Performed immediately after a build or deployment, or as part of continuous integration.

_Key differences:_

1. *Purpose*: Regression testing ensures changes didn't introduce new defects, sanity testing verifies overall functionality, and smoke testing checks critical functionalities.

2. *Scope*: Regression testing covers the entire application, sanity testing focuses on critical functionalities, and smoke testing is limited to high-risk areas.

3. *Depth*: Regression testing is in-depth, sanity testing is high-level, and smoke testing is basic.

4. *Frequency*: Regression testing is performed after changes, sanity testing after a build or deployment, and smoke testing immediately after a build or deployment.

By understanding these differences, you can apply the right testing technique at the right time to ensure your software application or system meets the required quality standards.

Do you have any further questions about regression, sanity, and smoke testing?