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9 Tips for selecting test cases for Regression Testing

Regression testing is selective retesting of a system or component to verify that modifications have not caused unintended effects in previously working modules of software/application. This type of testing is typically associated either as a ‘challenge’ or ‘unimportant’ by developers; but a good tester always enjoys breaking the software to scour out each and every fault from it. Having said that even regression testing can become a challenge for the testers as well. Here are some of the reasons:-

1. The Number of test cases in regression suite increases with each new feature.
2. Sometimes, the execution of entire regression test suite becomes difficult due to time and budget constraints.
3. Minimizing test suite while achieving maximum test coverage is not a cake walk.
4. Determination of frequency of Regression Tests after every modification or every build update or after a bunch of bug fixes is always a challenge.

The graph below depicts the same

 Hence selecting test cases for regression testing is quite a tricky task. Today, I am sharing some tips that I found to be most effective while selecting test cases for regression testing

Below are the 9 simple tips:-

1. Include the test cases which have frequent defects:
Some areas in product are so error prone that they usually fail with a small change in code. We can keep track of failing test cases due to such areas throughout the product cycle and cover them in regression test suite.

2. Include the test cases which verify core features of the product:
Prior to designing of the test cases figure out all core features of application. Ensure that, test case cover all functionality mentioned in requirement document. One can make use of traceability matrix to make sure that no requirement is left untested.
Example:- Client would never expect a Home Page/Login Page/Key functionalities of his application  getting failed.

3. Include the test cases for Functionalities which have undergone more and recent changes:-
SRS keeps on getting updated. Sometimes, the updates are not in full change to the previous SRS. But to some extent (may be 15-30 %) changes may happen for every version upgrade. We testers have to agree that, it’s difficult to keep writing (modifying) test cases, as the SRS keeps on getting updated often and this leads to some end moment internal defects and changes into the code which in turn might break some already existing functionalities, So it’s a “Must” (a must with capital M ) to always include such test cases which has recent changes.

4. Include all the Integration test Cases:
Even if Integration testing is a separate part of software testing cycle, its test cases should be included in regression test suite.
A last moment fix, in already tested application can break the integrity between different modules. For example, data might get lost across an interface, messages might not get passed properly or interfaces might not be implemented as specified.

5.  Include all Complex Test Cases:-
Some functionality of the system may only be accomplished by following some complex sequence of GUI events.
For example, to open a file a user may have to click on the File Menu and then select the Open operation, and then use a dialog box to specify the file name, and then focus the application on the newly opened window. Obviously, increasing the number of possible operations increases the sequencing problem exponentially. This can become a serious issue even if one of the steps is not working—A whole functionality comes to HALT, and End-User feels like a crap . That’s why all such complex test case should be included in regression test suite.

6. Prioritize the test cases for regression testing:
A stitch in time saves nine” …nay!!
We will go with “A SMART stitch in time (can) saves Ninety-nine

Prioritize the test cases depending on business impact, critical & frequently used functionalities. It is always helpful if some analysis is done to find out what test cases are relevant and what are not. It is a good approach to plan and act for regression testing from the beginning of project before the test cycles. One of the ideas is to classify the test cases into various Priorities based on importance and customer usage. Here it is suggested the test cases be classified into three categories;

Priority-0 Priority-1 Priority-2
Sanity test cases which checks basic functionality (as per the SRS of product) and are run for pre-system acceptance and when product goes through major change. These test cases deliver a very high project value to both engineers and to customers. This includes the test cases which tests essential functionalities that deliver high project value to both engineers and customers.  These are executed as a part of ST cycle and selected for regression testing on need basis. These test cases deliver moderate project value.

 

Selection of test cases based on priority will greatly reduce efforts spent on regression testing.

7. Categorize the selected test cases: –

Regression testing becomes very difficult when the application scope is very huge and there are continuous increments or patches to the system. In such cases selective tests needs to be executed in order to save testing cost and time. Categorizing test cases makes this work easier. We can categorize them as
1) Reusable Test Cases:
It includes test cases which can be repetitively used in succeeding regression cycles. This can be automated so that set of test cases can be easily executed on new build.
2) Obsolete Test Cases:
These test cases are defect specific and can’t be used in succeeding cycles. Smart way is to use them is when relative defect occurs.

8. Choose the test cases on “Case to Case” basis:

There could be several right approaches to regression testing which needs to be decided on “case to case” basis:

Case 1: If the criticality and impact of the bug fixes are LOW, then it is enough that a test engineer selects few test cases from TCDB (Test case DB) and executes them. These test cases can fall under any Priority (0, 1 or 2).

Case 2: If the criticality and the impact of the bug fixes are Medium, then we need to execute all Priority-0 and Priority-1 test cases. If bug fixes need additional test cases from Priority-2, then those test cases can also be selected and used for regression testing. Selecting Priority-2 test cases in this case is desirable but not a must.

Case 3: If the criticality and impact of the bug fixes are High, then we need to execute all Priority-0, Priority-1 and carefully selected Priority-2 test cases.

Case 4: One can also go through the complete log of changes that happened (can be obtained from Configuration management engineer) because of bug fixes and select the test cases to conduct regression testing. This is an elaborate process but can give very good results. I hope this will help you to find out what test cases should be included in your regression test suite.

9. Change the regression test cases whenever required.
RESET of test case is not expected to be done often. Resetting of the test cases needs to be done with following considerations;

a. When there is a major change in the product
b. When there is a change in the build procedure which affects the product
c. Large release cycle, where some test cases were not executed for a long time
d. You are in the final regression test cycle with a few selected test cases
e. When there is a situation where the expected results of the test cases could be quite different from previous cycles.

Having said that “No use of reinventing the wheel again“,

On similar lines why to execute test cases manually if we can automate them and reuse it?

In RT Task, including an automation suite is always painless and feasible as it covers a wide area of testing scenario. Infact Regression test suite should be 99.99% automated (It may require executing the RT task after every new build is fired).
Ahaa!! It sounds good, Running a test suite in night hours and getting test report in morning, what a start to your day, when you realize your half of the work is already done.

Guys, I hope this article will be useful for you. Correct me if I am wrong somewhere.
Contact Us: info@prototechsolutions.com

References:

1. isqtinternational.com/defect/images/2.doc
2. http://agile.csc.ncsu.edu/SEMaterials/BlackBox.pdf
3. http://www.ijaer.com/webmaster/upload/Apr_2012_Sheo%20Kumar.pdf

Author : Abhira K.

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ProtoTech Solutions is a custom engineering software development company with skills in 3D visualization on desktop/mobile/cloud. My role in the company is essentially Business Development and Marketing.

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