Regression Testing in a Nutshell: Why is it Important?

Software development is a constantly ongoing process. There's no such thing any more as a 'final' version, and as soon as one update hits production, you should already be working on the next.

However, if you aren't careful about how you manage the process of making changes, you can cause a range of problems. It might only take a relatively minor issue in an update, such as an incompatibility with existing code, for a chain reaction of failure to occur and the entire application to crash. Even in less severe cases, introducing new bugs to a piece of software creates many headaches for developers, as well as lots of unhappy users.

So how do you ensure that the next time you push an update live, it will work as intended? With regression testing.

What is regression testing?

Regression testing is a type of software test performed on existing applications that have recently undergone a change in code, such as an update or adding additional features. It's a key part of the quality assurance process and its purpose is to ensure all existing functionalities continue to work and aren’t negatively affected by the new additions or alterations.

It's important not to get confused between regression testing and retesting. The two terms may sound like they're describing the same thing, but actually there are important distinctions between them. While regression testing involves looking for issues, retesting refers to repeatedly testing specific bugs and defects that have already been found in the regression testing process to determine whether they've been fixed.

In other words, regression testing involves testing code that was working, but now might not be. Retesting, on the other hand, is testing code that you know wasn't working to see if it now is.

The main types of regression testing

There are several ways to perform regression testing, which generally either take a narrow focus on specific test cases, or a wider view that covers the entire program. Some of the common options within this range include the following:

Selective: Instead of testing the whole system, this looks only at specified components. Narrowing down to the most relevant units enables testing to be completed faster and at lower cost.

Partial: Partial testing is used for reviewing how certain changes in code impact the rest of the applications. In this type of testing, new and existing code are able to interact with each other, which is vital if you need to determine how additional code or updates will affect overall functionality.

Complete: A full regression test evaluates the entire system. This is the most costly and time-consuming type of testing and is often carried out when there are multiple changes to the existing code. This is usually the final stage in confirming that any changes won’t break the application before an update is pushed to end users.

Why is regression testing important?

Failure to perform thorough regression testing means you have no way of knowing whether your application's new version will be stable, and if you're waiting until bug or crash reports start coming in from end users, it's too late. Not only will this result in more wasted money and unplanned downtime while problems are fixed, by the time everything is working again, the damage may already have been done.

For instance, on mobile, 80% of apps are deleted after a single use, and one of the main reasons for this is problems such as performance or crashing. However, the impact could go much further than losing a single customer - 74% of users base their buying decisions on word of mouth, so the impact can quickly spread.

As well as keeping users happy, regression testing keeps your apps productive and cost-effective. Indeed, one study of the banking sector found successful regression testing cuts the time spent fixing bugs by 60% and offers financial savings of 40%.

When should you perform regression testing?

Regression testing can be conducted in a number of situations, but it's generally good practice to undergo these activities any time you're making adjustments to existing code or adding new lines to an application. Some times when it's essential to do this include the following.

• When implementing new code
• When changes are made to old code
• When fixing bugs
• When fixing performance issues
• When porting an app to another platform

Performing regression tests

In order to ensure the best chance of success for your regression testing, there are a few key steps you need to follow. Doing this ensures you're focusing on the right areas and not trying to do too much at once. Here are some basics to keep in mind.

Step 1 - Choose your test case: The first stage should be to make sure you're testing the right elements of your application. For instance, it's often a good idea to focus on areas in a program that are prone to defects or that frequently undergo updates or code changes.

Step 2 - Select your tools: There are a range of tools you can use to perform regression testing, which may not all be suited for the same tasks. For example, functional regression testing tools allow developers to test individual elements of a software program, whereas unit testing tools help you evaluate specific code elements within the application.

Step 3 - Focus on configuration: Set up configuration management solutions to ensure your test environment is isolated from other updates and make sure it's not going to be affected by any outside disruptions that could impact the results.

Once you've completed these steps, you can go ahead and execute the test using your choice of manual and automated tools. These should be able to produce a final report that gives a clear indication of each component and whether it's passed or failed.