Smoke and Regression Testing: In today’s world, software permeates every aspect of life. However, as systems become more complex and development speeds up, the risk of defects increases, leading to financial losses and a decrease in user trust.
According to industry research, a successful cyberattack costs the affected organisation an average of $11 million, not counting the additional costs of remediation and reputation restoration. This highlights the importance of early detection and remediation of vulnerabilities.
A study by the Florida Institute of Technology shows that organisations implementing systematic test automation achieved a 37% increase in productivity compared to manual testing methods. The study also confirms that automation reduced testing time by an average of 75% for regression testing scenarios, while improving defect detection by 30%.
This article will demonstrate the differences between smoke and regression testing, highlight situations in which each approach is most effective, and provide practical recommendations on how to use them to ensure the quality of a software product.
What is Smoke Testing?
Smoke testing is a basic software testing method that allows you to check the basic functionality of a system quickly. Its name comes from an engineering practice: if a device emits smoke when you turn it on, there is no point in conducting further tests. In software development, the analogy is this: if key features of an application fail to start or cause critical errors, no one will waste resources on a detailed investigation of an unstable or faulty build.
Therefore, the primary goal of smoke testing is to ensure that the basic functionality of a software product works after a build or change, without delving into each function.
Key Features
The smoke test has the following key characteristics:
- Local coverage, which tests the most critical functions of the system (e.g. startup, authorisation, interface navigation);
- Test automation for rapid release after each build;
- Speed, which minimises testing time;
- Deployment frequency
Surface Testing Methodology
Methodologically, smoke testing is a high-level, comprehensive test. It covers many features with minimal detail. This lets you determine whether the product is ready for regression testing, integration, or user validation. Test cases are developed by the web and mobile platform company during the planning stage and updated as the product evolves. They must be relevant and accurately reflect the critical uses of the system.
What is Regression Testing?
Regression testing is software testing that aims to verify that changes (such as bug fixes, new features, or updates) do not negatively impact current functionality. The process is systematic and thorough. It should prevent “regression,” which is the reintroduction of previously fixed defects or the introduction of new bugs in stable parts of the code. This is especially important in an agile environment where releases are frequent and reviews are performed periodically.
Software Regression Concept
The concept of software regression assumes that after changing the code in one place, errors occur in another, already tested part of the system. Dependencies between components, side effects, or incorrect integration of new functions can cause these errors. Testing helps to identify and minimise problems before the product reaches the end user.
Unlike superficial smoke tests, regression testing covers the most significant possible part of the existing functionality. It includes hundreds or thousands of test cases covering user scenarios and internal processes. Therefore, this tool is one of the most important for maintaining software quality.
Regression testing is often performed at all stages of the development cycle, from introducing new features to releasing a new version. Regular and systematic testing allows the development team to confidently move forward without fear of old errors reappearing or manifesting themselves in new conditions.
The concept is implemented as follows, for example:
- On the e-commerce platform, developers added a new module for calculating discounts for advertising campaigns.
- The new function worked correctly, but after implementation, a violation was discovered when calculating the total order amount when placing an order.
- The new module reused the general utility function, which was modified. This was only discovered during extensive regression testing.
- The situation was eliminated before the function was launched, which avoided potential losses and user complaints.
Deep Level Testing Methodology
The deep testing methodology uses a complete set of ready-made tests to check the system’s functions. These tests are performed manually or automatically to optimise the process and reduce the likelihood of human errors. Specialists sometimes use selective regression testing, assessing specific areas that may be affected by changes. As a result, regression testing becomes an essential means of ensuring the ongoing reliability and integrity of the software product at all stages of development.
Key Differences Between Smoke Testing and Regression Testing
How can we easily understand the difference between regression and smoke testing? There are five critical factors.
Timing and Frequency
Figuratively speaking, smoke testing acts as a quick filter at the input, and regression testing acts as a deep check at the output after any change to the system. In comparison:
- Smoke testing is performed early, after each continuous integration or integration build.
- Regression testing is performed after changes, fixes, updates, and before release.
- Compared to regression testing, Smoke testing is performed more frequently, daily or several times a day.
- Regression testing is performed regularly, but less frequently, once per sprint, before release.
Scope and Depth
Smoke testing helps you quickly understand whether you can continue working with the current build, while regression testing provides confidence that there are no bugs after making changes. Both approaches are essential, but they are used at different scales and with varying levels of evaluation.
- Smoke test does not aim to detect all errors and only focuses on critical functions: application launch, authorisation, page navigation, and other fundamental interactions with the user interface.
- Regression tests comprehensively cover all functions, such as user scenarios, interactions between modules, business logic, and checking of boundary conditions, interfaces, APIs, databases, and internal processes. This makes regression evaluation much deeper, more voluminous, and more labour-intensive than smoke checking.
Test Case Complexity
Simple test cases in the smoke review do not go deep into the logic or cover all scenarios. They aim to provide a minimum viable confirmation of the build’s stability before further in-depth assessment.
Examples of simple tests are:
- Check if you can enter the build.
- Check if the home page launches.
- Check the fundamental transitions between sections..
The number of tests is usually limited. Depending on the size of the project and the number of significant functions, it can vary from a few to dozens.
Extensive and detailed test cases in regression testing are more complex, thorough, and varied. They include positive and negative scenarios, boundary conditions, module dependency chains, and exceptional cases.
For example, it can be:
- Testing error handling for incorrect data input;
- Testing business logic in non-standard conditions;
- Checking interactions between different system components.
The number of tests can cover hundreds or even thousands of cases, especially in mature products with extensive functionality.
Execution and Responsibility
|
Aspect |
Smoke Testing |
Regression Testing |
| Who does it | Developers check the build stability before handing it over to QA.
QA confirms basic functionality. |
The QA team performs the main testing.
Test engineers support automation |
| Goal | Checking if the system starts and if there are any critical errors | Detecting errors that appeared after changes in the code |
| Collaboration | QA ↔ developers: sharing information about the build and critical bugs. Fast response to unsuccessful builds | Developers inform QA about changes in the code
QA adjusts test plans for sensitive |
| Role of Automation | Used on Mature Projects
Tests are built into CI/CD Instant Stability Check |
Necessary for Scalability
Ensures Fast, Accurate, and Repeatable Testing |
| Manual testing | Relevant at early stages
Quickly finds blocking errors |
Used locally (for example, for complex UI features), but the primary focus is on automation |
| Benefits of automation | Acceleration of processes
Increased reliability of assemblies |
Saving time and resources
Scalability High accuracy Fast feedback |
When to Use Smoke Testing
Smoke testing is used in various situations. This approach is most relevant after new builds or deployments, when critical errors need to be identified. This method is also appropriate for developers who practice continuous integration. They perform minimal testing before committing changes to the main code branch, preventing critical errors from penetrating the general code.
In addition, smoke testing filters out defective versions before starting a complete regression or functional check. This is a mandatory step in the CI/CD workflow in modern projects. Any changes to infrastructure, server configurations, and libraries always require a quick check of critical functionality.
Real-world examples and scenarios
There are several scenarios with examples of surface tests in real life.
- A common situation is when a QA specialist takes a new build of an online store and checks the loading of the main page, the function of adding a product, and the ability to pay for a purchase.
- When developers change the authorisation module, they must manually check how the user logs in after the changes.
- Another option: Playwright autotests are used in a project’s CI pipeline to check the site’s main pages’ availability and the correct loading of the primary API endpoints.
When to Use Regression Testing
Regression testing guarantees that new features do not disrupt existing system functionality. It is required after:
- Adding new features;
- Bug fixes;
- Code changes;
- Optimisation or refactoring;
- During major upgrades or transitions to a new platform.
Integrating APIs, third-party services, or internal modules requires regression testing to identify conflicts quickly. Even changes aimed solely at improving performance can affect the application logic, requiring mandatory diagnostics.
Examples and real-world scenarios
Let’s list the most common scenarios where in-depth product testing is used. For example, this could be the launch of a new version of a mobile banking platform. The team extensively tests authorisation, basic transactions, creating new accounts, and transaction history. An educational platform website implements page caching, and testers must check that new lessons, results, and profile updates are displayed correctly.
Pros and Cons
Smoke Testing
Pros:
- Quick check of build functionality;
- Early detection of critical defects;
- Saving time and resources at the early stages of testing;
- Possibility of automation of CI/CD processes;
- Reduced costs for complete testing of defective versions.
Cons:
- Only superficial functionality is tested, without identifying deeper defects.
- This sometimes creates a false sense of stability, as comprehensive checks are not performed.
- A limited set of tests does not cover all possible use cases.
- Tests need to be updated periodically when key functionality changes.
Regression Testing
Pros:
- The product is stable and consistent after changes are made.
- Testing reveals hidden defects and side effects of fixes.
- New versions are released without loss of quality.
- Possibility of automation and scalability.
Cons:
- Manual execution is time-consuming and resource-intensive;
- Test suites sometimes proliferate and require constant updating;
- Automation requires initial investment and test maintenance.
- If tests are unstable, there is a high probability of false positives.
Automation in Smoke and Regression Testing
Automation provides benefits for both types of testing:
- Speeds up processes;
- Harmonises results;
- Facilitates integration into CI/CD pipelines.
Smoke tests are quickly automated and are ideal for assessing build stability in continuous integration environments. For example, a team can run an automated smoke test suite of 20-30 tests in less than 5 minutes after each build and quickly decide whether to continue or roll back the check.
Regression tests are time-consuming and run more frequently, which requires automation. In large projects, manually running a full regression test suite can take several hours to a few days. After the publication of Capgemini’s Global Quality Report, it was found that over 60% of teams cite regression testing automation as a key factor in accelerating releases and improving product quality.
Best Practices and Recommendations
Experts from leading software testing companies recommend including smoke and regression testing in your quality assurance strategy. Here are some recommendations to help make testing more reliable and less routine for the team. They will also improve the quality of test cases.
- Keep scripts up-to-date, remove outdated tests (especially regression tests), and update expected results after the latest significant changes to the product.
- The test suite should include only the most critical scenarios responsible for the performance of key features. This will optimise testing and increase its value.
- The regression test suite should not contain duplicate tests. Redundancy is harmful because it increases support costs and execution time.
- The principle of “one test – one result” implies that each test evaluates a specific functionality, while general tests make it difficult to diagnose errors and automate.
- Negative scenarios in regression are necessary; they check the system’s behaviour under erroneous input data and incorrect actions.
- Using metrics and performance evaluation, prioritise and refine the test suite, i.e. track which tests find defects and which do not.
- The quality of test cases will be higher if the goals are defined and the preconditions, expected results, and context are documented. Scripts should be understandable to any team member, and the team should automate the most stable ones. This saves a lot of time and human resources.
Thus, the path to high software quality consists of many small but successful steps. Using smoke testing as a first filter and regression testing for thorough verification, teams create reliable products. These features complement each other in ensuring product quality, reducing risks and accelerating release. A systematic approach, automation and thorough verification turn complex projects into success stories.
FAQ
What is smoke testing with an example?
Smoke testing is a quick, initial review of the basic functionality of a system. It ensures that the application launches and its basic functions work correctly. This test is necessary before a more in-depth assessment.
An example of using smoke testing is updating a mobile banking application. The tester performs a basic check to ensure the application launches without errors. Can you log in using your username and password? Is your balance displayed on the home page? Does the money transfer function work? If there are critical issues, such as the application crashing after launch or you cannot log in to your account, the entire package is returned to the developers for fixing.
Is smoke testing a subset of regression testing?
Not exactly. Although these two types of testing overlap, they have different goals. Smoke testing involves quickly checking the most important features to ensure the application is ready for large-scale testing. Regression testing, however, involves thoroughly checking the system after changes or fixes have been made to identify new defects.
Thus, smoke testing is more of a preparatory stage than a subset of regression testing.
What is the difference between regression and sanity testing?
Regression and sanity testing are often confused, but they are different concepts. Regression testing is a large-scale testing of the entire system or its parts after making changes. Testers confirm that everything works correctly. Sanity testing is a quick, localised test of a specific functionality after making minor changes or fixing bugs. This way, testers ensure the fix does not affect other system parts.
In short, it can be described as follows: regression testing provides broad coverage, while sanity testing is a quick, step-by-step check. Both approaches are essential at different stages of product development.
Is smoke testing part of UAT?
No, smoke testing and UAT (User Acceptance Testing) are performed at different stages and have different objectives. During the development phase, smoke testing is performed earlier to ensure the system is fully operational. It is a basic technical check. UAT is performed in the final stage of the project, when the product is almost ready for release. End users or customers perform it to ensure the product meets business requirements and expectations.
In short, smoke testing prepares for more extensive testing, and UAT is the final check before market release.
What is the difference between smoke testing and retesting?
Smoke testing and retesting differ in purpose and are used at different stages. Smoke testing covers a broad but superficial range of checks and is aimed at quickly verifying the system’s basic functionality after a new build. Retesting is done after a specific bug or defect has been fixed and is designed to confirm that the problem has been solved. Retesting focuses on one or more particular scenarios related to the fixed bug.
Conclusion: Smoke testing generally verifies functionality, while retesting verifies the effectiveness of a specific fix.
Is smoke testing a subset of regression testing?
Smoke testing checks whether the product is functional, while regression testing checks whether it remains functional after completion. Smoke testing is a separate type of testing, not a subset of regression testing. Although smoke testing sometimes overlaps with basic regression testing scenarios, they are two approaches regarding purpose and depth.