How to test legacy app: Best practices to follow

Even as an increasing number of businesses are adopting digitisation to stay relevant and grow in a tech driven economy, the modernisation of legacy applications has become crucial. Despite being regarded as antiquated, legacy systems store huge databases, of customer records, financial ledgers and other sensitive corporate data. Hence, when adopting modernisation, it is critical to reach out to experts and ensure effective software testing is conducted to ensure not only loss of data but also cost-effective and efficient integration of systems which can help add business value for organisations.

To elaborate, the need for legacy application testing results from a number of factors, including but not limited to need for reducing the time to market for a product, maintenance and usage costs related to the technologies used in legacy applications, and other aspects like a reduced ability to automate routine manual tasks because of restrictions placed on technologies like mainframes and the tools available to do so. However, the testing process can be challenging and can be riddled with various hurdles, making it imperative that the task is carried out by experts who can operate and execute the programme, bring knowledge, expertise, and experience of particular processes, software techniques, and skill sets, as well as the choice of relevant tools. Some of key aspects that a software testing team needs to address include:

Determining potential information sources

Finding sources of knowledge about the system being tested is crucial because documentation can be hard to find or outdated. Since it is unlikely that one individual will have all the solutions, companies must be proactive in the quest for knowledge and assist the software testing team with all potential resources to ensure adequate knowledge transfer is conducted.

Understanding system dynamics for effective integration

Considering the complex dynamics of legacy and contemporary tech integration, its vital that the software testing experts are well acquainted of the nature of both the old and the new systems. Considering lack of documentation in some cases, it is important to have a team that can decipher and understand the system from a technical perspective and answer questions that can help with test automation. What are the most common environmental issues in the project? What are the biggest integration pain points related to system-to-system communication? Which aspects of the business logic are causing the most conduction?

Determine what should be automated and what shouldn't

Test automation can help in making lives easier in any project, especially when dealing with vast legacy application testing. On the other hand, automation is not a silver bullet that magically fixes all problems. It can actually make things more difficult, with even one wrong move. Trying to automate everything, automating without properly analysing the system under test, investing too much in UI automation, not taking into account complex system integrations, having unreliable test data, and working with unstable test environments are all examples of undesirable approach to test automation.

Best practices in legacy application testing

The desire for 100 per cent test coverage is a practice that developers should abandon:

Since companies are not testing regular code, developers cannot concentrate on achieving 100 per cent coverage. Unit testing for legacy code in general. Legacy codebases are enormous and intricate. Focus on 'large' tests like integration and functionality tests instead of making an effort to test every loop in every method of every class. Frequently changing contexts and making sure all of the tests pass without altering the model code as usual.

Application usability and efficiency needs to be at the core of modernisation

When embarking on legacy application testing, there needs to be a clear understanding to not lose out on or diminish the usability/ efficiency of the application. Often, testers can get so engrossed in the process and assume that modernising it will automatically equal to enhanced efficiency, that the presumption can lead to massive setbacks.

Include testing in your CI/CD process

CI/CD pipelines make sure that every check-in to the code repository triggers the execution of automated tests and that new changes don't damage current functionality. Continuous Integration (CI) enables businesses to release new features more quickly. Using any language or tooling companies like, create a set of tests (test suite) for each class in the legacy application.

Investing in technical documentation

Technical documentation is best practice in software development as a whole, although most businesses provide it for the following reasons: Whenever a rewrite is required, or an existing feature has been altered. While enhancing already-existing features and introducing new ones; the biggest problem that documentation addresses is how much less work is required for upkeep and the creation of new features.

This general approach can help a legacy project significantly increase test coverage and comprehension. Once you have a baseline, you can restructure the application with the assurance that you aren't breaking anything by using other software development techniques. The objective is to standardise the application to the point where you can begin to rely more on industry standards and characterization testing. When you get to that point, you can begin to remove the harness because it has served its purpose.

(The author is CEO and Co-Founder of Goavega Software Pvt Ltd)