Mainframe Testing Best Practices

The mainframe systems are high-speed and high-performance systems. They are used for large-scale processing, mainly in banking and finance industries that deal with huge amounts of data. Here, mainframes are used as they are highly scalable, reliable, and secure, and they are much more capable than the regular computers we use.

So, mainframe testing is the process of testing mainframe software to make sure it works well on mainframe systems. Also, that it has optimum software reliability, quality, and performance. It verifies software, applications, and services that are part of the mainframe system. Once all these entities are verified using mainframe testing, the app is ready to launch in the market. Mainframe testing uses various verification approaches and validation techniques for this purpose.

Various automation tools/platforms are available today for mainframe testing. In addition to using various attributes and methodologies, it is important to consider best practices for mainframe testing to ensure its effectiveness and satisfactory results.

This article will discuss some of the best practices to follow when performing mainframe testing.

Understanding Mainframe Testing

Mainframe testing involves validating applications, services, and systems on the mainframe infrastructure. It ensures that changes, new deployments, and updates function correctly without disrupting existing business processes. Mainframe testing covers:

● Functional Testing (validating business logic)

● Regression Testing (ensuring new changes don’t break existing functionality)

● Integration Testing (verifying interactions between systems)

● Performance Testing (measuring speed and efficiency)

● Security Testing (assessing vulnerabilities)

Testing in mainframe environments often deals with batch processing, online transaction processing (OLTP), databases like DB2, IMS, VSAM files, and legacy coding languages like COBOL, PL/I, and Assembler.

Challenges in Mainframe Testing

Before we discuss best practices, it's essential to understand the common challenges:

● Lack of Skilled Resources: Mainframe expertise is becoming rare as veteran professionals retire.

● Complex Legacy Systems: Many applications have evolved over decades without modern documentation.

● High Transaction Volumes: Testing needs to replicate the real-world load accurately.

● Integration with Modern Platforms: Hybrid environments can complicate testing scenarios.

● Limited Automation: Traditional manual testing dominates, increasing effort and risk.

Addressing these challenges with strategic best practices can greatly improve outcomes.

Best Practices for Mainframe Testing

The critical best practices to follow during mainframe testing are shown in the following figure.

Let us discuss the above best practices now.

1. Perform Dry Run of Job: Use empty input files and perform a dry run of the jobs to check that the tests affect every job in the system. This is good practice, as you can verify that the job is impacted by the changes in the test cycle.

2. Complete Test Task Setup: The entire test task setup should be completed before starting the test cycle. Getting the test task set up and ready will aid in the early detection of JCL errors, thus saving execution time.

3. Set Auto-commit to NO: When accessing DB2 tables through SPUFI (option set in emulator for accessing DB2 tables), set auto-commit property to “NO”. This will avoid unintentional updates to the database.

4. Confirm Technical Inventory: Project and test management are critical to the success of mainframe testing. The projects usually focus on applications that are important to business. Hence, always ensure that the technical inventory is up to date. All the technical resources, inventory, and test and use case data should be ready beforehand. Especially during mainframe migration, you have to confirm the technical inventory and ensure availability of test and use case data, as these two are critical for project success.

5. Create Required Data in Advance: It is a good practice to create the test data required for the testing before the test cycle begins. The test data should also be complete, as incomplete or inadequate test data may result in wrong results. Availability of test data is the primary challenge, especially in batch testing. So, prepare a complete set of data in advance.

6. Check All Outputs: In some cases, jobs may run successfully but not produce the correct output. For example, in the case of a batch run, MAX CC 0 indicates that the job has run successfully. But it does not necessarily mean the functionality is working fine, and the output obtained is correct. It is quite possible that the job execution is successful, but the output is empty or not as expected. Hence, it is always best practice to check generated outputs before concluding that the job execution is successful.

Following these best practices during mainframe testing make sure that the system functions efficiently when deployed or launched.

Best Practices for Specific Mainframe Testing Types

The following are the best practices for mainframe testing types

Common Mistakes to Avoid in Mainframe Testing

When mainframe testing is underway, mistakes are bound to happen unknowingly. Though we cannot avoid such errors, we can always remain cautious and avoid some common mistakes.

● Neglecting Documentation: Always document test cases, system flows, and lessons learned.

● Over-reliance on Manual Testing: Scale cannot be achieved without automation. Read: How to automate mainframe testing using AI.

● Ignoring Environment Constraints: Testing in unrealistic environments can lead to false positives.

● Delaying Integration Tests: Leads to costly late-stage defect discovery.

● Underestimating Security: Security should be embedded from the beginning, not as an afterthought.

Conclusion

The best practices for mainframe testing discussed here help that the mainframe system is thoroughly ready for deployment when testing is completed. These best practices also make sure that the various steps of the testing are effective. For example, one of the best practices is to check for all outputs. When the mainframe tester follows this practice, they can ensure that when the mainframe system is deployed in the market, there is a negligible chance of failure due to erroneous outputs.

By following the best practices outlined above—focusing on early testing, strong data management, intelligent automation, continuous performance monitoring, and skill development—organizations can ensure their mainframe systems remain robust, secure, and future-proof.

The goal is not merely to maintain legacy systems but to modernize testing approaches, making mainframe testing an agile, efficient, and value-driven discipline.