1. Regression testing is a type of software testing that seeks to uncover new software bugs, or regressions, in existing functional and non-functional areas of a system after changes such as enhancements, patches or configuration changes, have been made to them.
When to do regression testing?
Reasonable amount of initial testing is already carried out.
A good number of defects have been fixed
Defect fixes that can produce side-effects are taken care of.
Regression testing should be done periodically.

2. Methodology for RT
Performing an initial “smoke “ or “sanity test

3. Smoke testing
Smoke testing term came from hardware testing, when you get new hardware and power it ON if smoke comes out then you do not proceed with its testing. In software testing, a smoke test is run on application initial builds to ascertain application most critical areas are working correctly and application is ready for thorough testing.
Sanity testing
Once a new build is received after minor changes, instead of starting its complete testing sanity test is conducted to make sure previous defects has been fixed and new issues have not been introduces by these fixes. Sanity testing is a subset of regression testing.

4. 2. Understanding the criteria for selecting test cases
Two approaches for selecting test cases
Constant set of regression tests that are run for every build or change.
Selecting test cases dynamically
Selecting test cases requires knowledge of
Defect fixes and changes made in the current build
The way to test the current changes
The impact that the current changes may have on other parts of the system and
The ways of testing the other impacted parts.

5. Include test cases that have produced the maximum defects in the past.
Include test cases for a functionality in which a change has been made.
Include test cases in which problems are reported.
Include test cases which covers the mandatory requirements of the customer.
Include test cases to test the positive test conditions.
Include the area which is highly visible to the users
NOTE:RT should focus more on the impact of defect fixes than on the critically of the defect itself.

6. 3. Classifying test cases
It is important to know the relative priority of test cases for a successful test execution
Fixing priority based on importance and customer usage
Priority 0- These are called sanity test cases checks the basic functionality
Run for accepting the build for further testing
Run when a product goes through major changes
It delivers a very high project values to – Development teams and the customers

7. Priority 1
It delivers a very high project values to – Development teams and the customers.
Priority 2
It delivers moderate project values. ( it will be used for regression testing on a need basis)

8. 4. Methodology for selecting test cases
Critical and impact of defect fixes
Selection of test cases
Additional test cases
Low
Few test cases from TCDB ( TEST CASE DATA BASE) -
Medium
All Priority 0 and Priority 1 test cases
Test cases from priority 2 is desirable but not necessary
High
Subset of Priority 2 test cases

9. Critically
Impact
Low
Medium
High P0
Subset P1 P2 P0
All P1 P2
Very few P0
All P1 P2
Subset

10. If there is not enough time and the risk of not doing an impact analysis is low, then alternative methodology
Regress all: P-0,1,2 test case are run- all test cases are executed.
Priority based regression : P- 0,1,2 are run in order based on the availability of time- when to stop is based on availability of time.
Regress changes: code changes are compared to the last cycle of testing and test cases are selected based on their impact on the code.
Random regression: Random test cases
Context based dynamic regression: Few P-0 test cases are selected

11. 5. Resetting the test cases for regression testing
Selecting test cases based on test case result history – Information about test cases are recorded in each cycle is called TCRH.
In many organization – Not all the types of testing nor all the test cases are repeated for each cycle.
Test case history – what test cases and when??
Reset procedure : the method or procedure that uses tch to indicate some of the test cases be selected for regression testing is called reset procedure.

12. Points to be considered – Retesting
When there is major changes in the product.
changes in the build procedure which affects the product
Some of the test cases not executed for a long period
When the product is in the final regression test cycle with a few selected test cases.
expected result of the test cases is quiet different from the previous test cycle.

17. 6. Concluding the results of regression testing

18. Best practices in regression testing