Regression testing: a complete guide

Regression testing is a type of software testing that involves the re-execution of both functional and non-functional tests. The primary aim is to guarantee that both existing and newly introduced functionality within an application continue to work seamlessly and remain intact after updates or any other code changes. The term "regression" denotes "the return to a former or less developed state."

In practice, regression testing is typically performed shortly after a developer introduces new functionality or resolves a current bug in an application. Recognized as one of the most pivotal aspects of the overall testing process, regression testing holds a prominent position among various testing methodologies.

This article delves into the definition of regression testing, its purpose, distinctions from re-testing, the various types of regression testing, optimal timing for its execution, available tools, as well as the advantages and disadvantages associated with this method.

Table of contents

• What is the purpose of regression testing?
• Retesting vs regression testing
• Types of regression testing
• When to perform regression testing
• Automated regression testing versus manual testing
• Regression testing tools
• How to write regression test cases
• Advantages and disadvantages of regression testing

What is the purpose of regression testing?

If your business relies on an application or another software product, it's crucial to ensure that everything functions as intended. Even the slightest change in the code can have disastrous consequences, particularly if the product is already in use by customers. Regression testing serves as a protective measure against such risks.

Regression testing aims to: 

• Detect unintentional defects by identifying any unintended defects or problems that may have arisen during the software development or modification process.
• Ensure stability by detecting unexpected system behavior or issues, contributing to the overall stability of the software.
• Reduce risks by minimizing potential risks associated with changes, safeguarding against adverse effects on existing functionalities.
• Facilitate continuous testing, enhancing the overall quality and stability of the software.
• Enable early defect identification, preventing additional costs related to bug fixing in the future by identifying defects earlier in the software development lifecycle
• Ensure continuous development and improvement, ultimately leading to faster product delivery to the market.

Regression testing is particularly vital in Agile development, where speed is paramount. With short sprint cycles, developers introduce specific features in each cycle. However, every new feature requires testing to ensure it doesn't conflict with previously written code. This is where regression testing becomes indispensable. In Agile development, regression testing serves as a key quality assurance tool, ensuring the integrity of the software is upheld throughout the development lifecycle.

Retesting vs regression testing

Distinguishing between retesting and regression testing is key. While retesting focuses on correcting specific defects identified in failed test cases, regression testing ensures the overall application functionality is intact after changes, preventing unintended consequences.

In essence, retesting focuses on correcting known defects, while regression testing ensures the broader functionality of the application, safeguarding against unintended issues introduced by changes.

Types of regression testing

In software development, various types of regression testing cater to different aspects of the development lifecycle. Here are several notable types:

Corrective regression testing:

• Used when no changes are made to the source code or product specifications
• Reuses all test cases, requiring less time to find errors and minimizing testing costs

Complete regression testing:

• Performed when numerous changes are made to existing code, often before product launch
• Time-consuming but highly effective in detecting unexpected problems

Partial regression testing:

• Executed when merging new code with existing code to ensure the system works seamlessly
• Time-consuming, particularly for large code bases, but crucial for preserving existing functionality

Progressive regression testing:

• Applied during application updates to ensure existing features remain intact
• Performed when new test cases are developed and changes are made to program specifications

Retest-all regression testing:

• The most comprehensive type, re-executing all test scenarios to compare results with previous testing
• Time-consuming and complex, suitable for detailed testing of all functionalities

Selective regression testing:

• Executed when adding new code, selectively applying test cases to the newly added code
• Requires manual effort but saves time by testing individual components instead of the entire system

Unit regression testing:

• Conducted at the unit testing stage, isolating code components for usability testing
• Ideal for early error detection, saving time and resources in later stages of the software development lifecycle
• Can serve as project documentation and is particularly effective for small-scale tests

Each type of regression testing addresses specific needs within the software development process, contributing to the overall quality and stability of the application.

When to perform regression testing

Ideally, regression testing should be conducted in the following scenarios: when adding new features or functionality, when integrating with other products, and when making changes to existing functionality. 

Regression testing helps identify and rectify compatibility issues that could arise when new features or functionality are added or when integrating with another program. It also ensures that changes to the existing code do not adversely affect other aspects of the system. 

In the process of selecting the optimal approach to regression testing, it is crucial to consider the scope and impact of the update. When deciding between automation and manual testing, it is essential to allocate test cases based on the nature of the changes and the testing requirements.

Additionally, conducting risk analysis is a key step. This involves analyzing risks based on the project's scale, complexity, and importance. The insights gained from the analysis help tailor the regression testing approach accordingly.

Automated regression testing versus manual testing

Regression testing can be executed using either manual testing or automated testing tools. Each approach has its own advantages and considerations.

Automated regression testing offers several advantages. First and foremost, it excels in terms of speed and efficiency, surpassing manual testing in terms of rapid execution and resource utilization. This translates to a reduction in testing time and costs, coupled with the ability to achieve extensive test coverage. Another significant benefit is consistency; automated tests ensure the uniform execution of test cases, minimizing the risk of human errors. This makes automated regression testing particularly valuable for applications undergoing frequent changes, as the tests can be swiftly adapted to validate new functionalities.

However, there are considerations to bear in mind. Automated testing may encounter difficulties when dealing with a complex user interface, potentially making manual testing a more suitable option in such cases. Additionally, the implementation of automated regression testing requires a substantial upfront investment of time and resources, which may pose challenges for projects operating with limited budgets.

On the flip side, manual regression testing has its own set of advantages. It provides flexibility, making it well-suited for applications featuring intricate user interfaces or scenarios that prove challenging to automate effectively. Moreover, when faced with budget constraints, manual testing may emerge as a more viable option due to its lower upfront investment.

Yet, manual testing comes with its own considerations, too. It tends to be slower and less efficient compared to automation, which can be a hurdle when dealing with large and repetitive regression test suites. It may work well for small products, but as the number of features in the product grows, the time required for manual regression testing increases exponentially. The human element introduces the risk of errors, and the consistency of test execution may vary, posing challenges in maintaining a standardized testing process.

Consider automated regression testing when applications undergo frequent changes, and swift, consistent testing is crucial, especially if the project budget allows for upfront automation investment or as the test suite grows over time. Opt for manual regression testing when dealing with complex user interfaces or limited budgets, supplementing automated tests to achieve complete test coverage.

Regression testing tools

Choosing a regression testing tool depends on various factors such as capabilities, needs, objectives, preferences, and experience. Here are key considerations when selecting a tool:

• CI/CD pipeline support: Integration with CI/CD pipelines ensures seamless execution of tests, facilitating collaborative work and centralized issue debugging.
• Parallelization: For a large number of tests, parallelization is essential to save time and accommodate multiple test runs by development teams.
• Simplicity of scripts: In cases where the number of regression tests is substantial, a tool that simplifies the scripting process is preferable.
• Ease of maintenance: Tools that are easier to maintain save time and effort for testers in the long run.
• Good reporting: Comprehensive reporting benefits both developers and managers, providing insights into test results and aiding issue identification.
• Application compatibility: Some tools are designed for web applications, while others are suitable for desktop or mobile applications.
• Open source vs commercial: Evaluate whether an open-source tool or a commercial tool with licensing requirements aligns with the project's needs and available budget.

The choice of a regression testing tool hinges on the specific requirements of the project, including the type of application, desired automation level, and budget constraints.

Below are some of the popular tools.

Selenium

Selenium is a robust open-source web testing tool with extensive market experience, specializing in browser automation. It supports multiple programming languages, browsers (including mobile), and platforms. Selenium Grid facilitates simultaneous test execution, and it integrates seamlessly with popular testing frameworks such as JUnit and TestNG. The tool's capabilities can be further extended using plugins and extensions.

Katalon Studio

Katalon Studio is an automated testing tool leveraging Selenium and Appium frameworks for web, API, mobile, and desktop systems. It offers seamless integration with CI/CD frameworks like Jira, Jenkins, and Selenium Grid. Katalon Studio features a user-friendly interface, flexible support for various testing methodologies, and an active global community. While it requires commercial licensing, it provides both free and paid plans, including cloud and local versions.

Watir

Watir, short for Web Application Testing in Ruby, is an open-source testing framework using the Ruby programming language. It offers a user-friendly API for interacting with web elements and simulating user actions. Despite limited language support and cross-browsing capabilities, Watir boasts an intuitive API and has strong community support. The tool is free and web-based.

TestComplete

TestComplete is an automated UI testing tool designed for creating functional tests across desktop, web, and mobile applications. It supports parallel execution of regression tests with automated builds and efficient debugging capabilities. TestComplete is known for automating regression test planning and execution without manual intervention, making it suitable for GUI testing. However, it may require some manual steps to update test cases. The tool is locally installed on desktop or virtual machines.

Playwright

Playwright is a versatile web testing and automation framework that allows testing Chromium, Firefox, and WebKit using a single API. It supports cross-browser and cross-platform testing, including Windows, Linux, and macOS. Playwright is cross-language, supporting TypeScript, JavaScript, Python, .NET, and Java. Notable features include native mobile emulation, auto-waiting for usability, and the ability to create scenarios spanning multiple tabs, sources, and users.

Cypress

Cypress is an open-source automation tool written in JavaScript, emphasizing ease of use and providing a visual interface for running tests. It supports various test types, including end-to-end, component, integration, and unit tests. Cypress stands out with features like time travel, debugging directly in Developer Tools, automatic waiting for commands, and capturing screenshots and videos on test failure. It also facilitates cross-browser testing, supporting Firefox and Chrome family browsers, including Edge and Electron, locally and in CI pipelines. Cypress Cloud's Unreliable Test Management feature helps detect and diagnose unreliable tests.

How to write regression test cases

Before conducting regression testing, a comprehensive plan should be developed, serving as a roadmap for testers to follow throughout the testing process. This plan enhances overall efficiency and effectiveness, ensuring that regression testing aligns with project requirements. 

When writing a regression testing plan, determine the scope of testing work by defining the specific functionalities and areas of the application to be covered. Be sure to clearly state the objectives of the test, outlining what needs to be achieved through the testing process. You’ll need to identify all the resources needed for regression testing, including team composition, tools, and equipment. You should also establish a testing schedule with defined stages, deadlines, and dependencies. 

You will need to specify the test environment requirements (encompassing hardware, software, network configurations, and any other dependencies) as well as the testing methods to be used during the testing process. Lastly, outline regression testing deliverables, including test reports, defect reports, and documentation.

When writing regression test cases, it is essential to include test cases that cover the functionality affected by changes, critical features, and areas where defects are more likely to be found. 

To streamline the regression testing process, avoid including redundant or outdated test cases that do not contribute value. Skip tests that are unrelated to software changes or those with low defect detection probability or priority. This focused approach ensures that regression testing remains efficient and effective in validating the software's stability and functionality.

Before starting regression testing, ask:

• What changes have been made, and what functionality is affected?
• Which critical application functionality needs thorough testing?
• Are there specific priorities or timelines for regression testing?
• Are there specific test data or environment requirements?
• Are specific tools or techniques needed during regression testing?
• Are there specific requirements for results or documentation?

Efficient testing strategies involve identifying tests suitable for automation, prioritizing speed and reliability. Automate repetitive tasks, but for complex sequences or graphical interfaces, consider manual testing. Maintain clear communication within the testing team by separating manual and automated testing. This avoids confusion and establishes a structured reporting system. Each approach has its unique insights, and this distinction helps streamline responsibilities, fostering a more organized and effective testing process.

Test case example: user login regression test after application update

Test description: Verify that the user can successfully log in to the web application after a recent update.

Preconditions:

• The web application has undergone an update, and the updated version is deployed and accessible
• The user account exists with a known username and password
• No active user sessions are present

Test steps:

• Open the web browser and navigate to the login page
• Enter a valid username and password
• Click the "Login" button

Expected result: The user should be redirected to the home/dashboard page, indicating a successful login. The user's name or profile icon should be visible to confirm that the correct user is logged in.

Postconditions:

• The user is on the home/dashboard page
• The user is logged in, and their name or profile icon is displayed
• A session for the user is established

Pass criteria: The user is redirected to the home/dashboard page, and their name or profile icon is visible, indicating a successful login.

Fail criteria: The user is not redirected to the home/dashboard page, an error message is displayed, or the user's name/profile icon is not visible.

This test is conducted specifically after an update to the web application. The goal is to ensure that changes made during the update have not adversely affected the login functionality. This test focuses on the stability of the login functionality, which is critical for user interaction. By comparing the results with the expected outcomes, this test serves as a baseline for the login functionality post-update. Any deviation from the expected results indicates a potential regression.

Advantages and disadvantages of regression testing

Regression testing, like any methodology, comes with both strengths and weaknesses. Understanding these aspects is crucial for evaluating its suitability within an organization.

Advantages of regression testing

Regression testing is beneficial because it: 

• Detects new bugs introduced by code changes, revealing bugs and defects that were created as a side effect of code modifications and preventing future issues
• Verifies existing functionality, assuring that the rest of the software still works as expected and that changes didn’t break what already worked
• Reduces risk of updates by catching regressions quickly, allowing developers to address them before releasing updated code and create more stable software releases
• Increases confidence in changes so developers can safely release modified code without unintended consequences
• Facilitates frequent releases, enabling developers to release changes and improvements more frequently since they have tests to verify quality
• Reduces time and cost of troubleshooting by finding and fixing bugs earlier in the process 
• Increases efficiency by using automated regression test suites that can be rerun quickly and frequently
• Provides documentation by acting as living documentation of the system's intended functionality

Disadvantages of regression testing:

While there are many advantages to regression testing, it’s not without its challenges, including the following: 

• Time-consuming execution of large test suites can slow down development cycles
• Increased maintenance costs due to the need for regression tests to be continuously updated and maintained along with any changes to the software
• Complex test environments that may require complex test setups that are expensive to replicate and maintain
• False failures for reasons unrelated to new regressions, such as test data issues or environment differences
• Incomplete testing coverage that lack sufficient breadth and depth of coverage could lead to critical areas being missed 
• Automation challenges could require significant upfront investment and framework maintenance
• Prioritization problems compounded by limited resources could make testers struggle to prioritize what and when to test
• Isolating regressions can be difficult, it may be challenging to isolate the exact cause and whether old or new code is responsible.
• Overconfidence could lead to underinvestment in other testing such as exploratory testing

So while regression testing is very beneficial, it does come with overhead costs and risks like any testing strategy. Organizations must balance those tradeoffs based on their constraints and objectives.

When evaluating regression testing for your organization, prioritize based on the nature of changes in the application — frequent and significant changes make regression testing crucial. 

Assess the feasibility of automation, weighing its potential efficiency benefits. Consider project timelines; balance the benefits of regression testing against potential delays. Evaluate resource availability, both human and technological, and ensure the testing team possesses the expertise needed to execute regression testing effectively.

By weighing these factors, organizations can make informed decisions about incorporating and optimizing regression testing in their development and testing processes.

Elevate software stability with regression testing

In the dynamic landscape of software development, the importance of regression testing is unmistakable. Beyond just pinpointing errors, this essential methodology safeguards the stability and integrity of applications amid ongoing changes and updates.

Regression testing acts as a protective barrier, uncovering unintended defects, minimizing risks linked to modifications, and fostering the overall stability of software. Its contributions to early defect identification and continuous development are invaluable, especially in Agile environments characterized by short sprint cycles.

Developing effective regression test cases is a strategic endeavor, underscoring a comprehensive plan that encompasses scope, objectives, schedule, resources, test environment, methods, and deliverables.

In summary, regression testing serves as a linchpin for attaining software excellence. Its proactive role in ensuring stability and mitigating risks positions it as an integral component of the software development lifecycle. Organizations are encouraged to assess its suitability based on their specific needs, acknowledging regression testing as a foundational element for software reliability amid continuous evolution.