When to Automate: Smoke and Regression Testing

In the modern world, software permeates all areas of life. However, as systems become more complex and development accelerates, the risk of defects that lead to financial losses and a decrease in user confidence increases.

According to industry research, a successful cyberattack costs the affected organization an average of $11 million, not including additional costs for eliminating the consequences and restoring its reputation. This emphasizes the importance of timely detection and elimination of vulnerabilities at the early stages of development.

Research from the Florida Institute of Technology demonstrates that organizations implementing systematic test automation achieved productivity improvements of 37% compared to manual testing approaches. The study further documents that automation reduced testing time by an average of 75% for regression testing scenarios while improving defect detection by 30%.

This material will show the differences between smoke and regression testing and highlight in which situations each approach is most effective. It will also provide practical recommendations on how to apply them to ensure the quality of a software product.

What is Smoke Testing?

Smoke testing is an entry-level software review method aimed at quickly checking the basic functionality of a system. The name comes from an engineering practice: if smoke comes out of a device when it is turned on, further checking is pointless. In software development, the analogy is as follows: if the key functions of an application do not start or cause critical errors, no one will waste resources on a detailed study of an unstable or non-working build.

Thus, the main goal of a smoke check is to ensure the main functionality of a software product after assembly or changes without elaborating on each function in depth.

Key Features

The smoke test has the following key characteristics:

• Superficial coverage, when the most critical functions of the system are checked (for example, startup, authorization, interface navigation);
• Test automation for quick launch after each build;
• Speed, minimizing test time;
• Frequency of implementation.

Surface Testing Methodology

Methodologically, a smoke test is built as an "end-to-end" test at a high level. It covers many functions but with minimal detail. This answers whether the product is ready for regression, integration, or user validation. Test scenarios are developed by a web and mobile development company during the planning phase and updated as the product evolves. They must remain current and accurately reflect the critical ways in which the system is used.

What is Regression Testing?

Regression assessment is a type of software verification that aims to verify that changes made (such as bug fixes, new features, or updates) should not negatively affect current functionality. The process is systematic and in-depth. It should prevent "regression," that is, the reappearance of previously fixed defects or the appearance of new failures in stable parts of the code. This is especially important in an Agile environment where releases happen frequently, and revisions are made regularly.

Software Regression Concept

The concept of software regression suggests that there are situations when errors occur in another already tested part of the system after modifying the code in one place. Such errors can be caused by dependencies between components, side effects, or incorrect integration of new functions. Tests will help to identify and minimize problems before the product reaches the end user.

Unlike superficial smoke testing, regression testing covers as much of the existing functionality as possible. It includes hundreds or thousands of test cases covering user scenarios and internal processes. Therefore, this tool is one of the most important in maintaining software quality.

Regression verification is often performed at all stages of the development cycle, from introducing new features to releasing a new version. Regular and systematic tests allow the development team to confidently move forward without fear that old errors will return or begin to manifest themselves in new conditions.

The concept is implemented as follows, for example:

• On an e-commerce platform, developers added a new module for calculating discounts for advertising campaigns.
• The new function worked correctly in isolation, but after deployment, a violation of the calculation of the total order amount was discovered during checkout.
• The new module reused the general utility function, which was changed. Only thorough regression testing revealed this.
• The situation was resolved before the function was released into production, and this prevented potential losses and user complaints.

Deep Level Testing Methodology

The deep-checking methodology involves using a full set of tests previously created to check various system functions. These tests are either performed manually or automatically to speed up the process and reduce human errors. Specialists sometimes practice selective regression, where they test selected areas that could be affected by changes. As a result, regression evaluation becomes an important protective measure that ensures the continuous reliability and integrity of the software product throughout all iterations of its development.

Key Differences Between Smoke Testing and Regression Testing

How can we easily understand the difference between regression and smoke testing? There are five important factors.

Timing and Frequency

Figuratively speaking, smoke review acts as a "quick filter" at the input, and regression testing acts as a "deep check" at the output after any modifications to the system. For comparison:

• Smoke checking is performed in the early stages after each build or CI integration.
• Regression verification is performed after changes, fixes, updates, and before the release.
• Smoke testing vs regression testing is performed more often, daily, or several times daily.
• Regression tests are performed regularly, but less often, usually once per sprint, before the release.

Scope and Depth

Smoke tests help you quickly understand whether you can continue working with the current build, while regression tests provide confidence that nothing has broken after making changes. Both approaches are important but are used at different scales and with different evaluation depths.

• Smoke test does not aim to detect all errors and only focuses on critical functions: application launch, authorization, page navigation, and other basic 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 labor-intensive than smoke checking.

Test Case Complexity

Simple test cases in the smoke review do not go deep into the logic and do not 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:

• Checking if the build can log in;
• Checking if the home page launches;
• Checking basic transitions between partitions.

The number of tests is usually limited. Depending on the size of the project and the number of major features, they can range from a few to dozens.

Extensive and detailed test cases in regression assessment are a more complex, detailed, and diverse process. It includes both positive and negative scenarios, boundary conditions, chains of dependencies between modules, and rare cases.

For example, it can be:

• Tests of error handling in case of incorrect input;
• Tests of business logic under non-standard conditions;
• Verification of interactions between several system components.

The number of tests can number hundreds or even thousands of cases, especially in mature products with wide functionality.

Execution and Responsibility

When to Use Smoke Testing

Smoke testing is used in several specific situations. This approach is most appropriate after new builds or deployments when it is necessary to identify the presence of critical errors. The method is also relevant for developers who practice continuous integration. They do minimal tests before committing changes to the main code branch, thereby preventing critical bugs from getting into the general code.

In addition, shallow tests filter out broken versions before starting a full regression or functional check. In modern projects, they are a mandatory stage of the CI/CD pipeline. Any changes to the infrastructure, server settings, and libraries will 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 authorization 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 main API endpoints.

When to Use Regression Testing

A regression test is performed to ensure that new features do not disrupt the existing functionality of the system. It is required after:

• Adding new features;
• Fixing bugs;
• Code changes;
• Optimization or refactoring;
• During major updates or transitions to a new platform.

Integrating APIs, third-party services, or internal modules also requires regression evaluation to detect conflicts promptly. Even changes aimed only at improving performance can affect the application's logic, so they require mandatory diagnostics.

Examples and real-world scenarios

Let's list the most common scenarios when deep product assessment is used. For example, this could be the release of a new version of a mobile bank. The team fully tests authorization, basic transactions, creating new accounts, and transaction history. Page caching is being implemented on the educational platform's website, and testers need to check the correctness of the display of new lessons, results, and profile updates.

Pros and Cons

Smoke Testing

Pros:

• Quickly checks the "viability" of the build;
• Early detection of critical defects;
• Saving time and resources at the early stages of assessment;
• Possibility of automation in CI/CD pipelines;
• Reduces the cost of full verification of non-working versions.

Cons:

• Only superficial functionality is checked without identifying deep defects;
• Sometimes, it gives a false sense of stability, because there are no full-fledged checks;
• A limited set of tests does not cover all possible use cases;
• Tests are required to be regularly updated when key functionality changes.

Regression Testing

Pros:

• The product is stable and consistent after changes;
• Tests show hidden defects and side effects of fixes;
• New versions are released without loss of quality;
• Possibility of automation and scaling.

Cons:

• Manual execution requires a lot of time and resources;
• Test sets sometimes grow quickly and require constant updating;
• Automation means attracting initial investment and test maintenance;
• False alarms are likely if tests are unstable.

Automation in Smoke and Regression Testing

Automation provides benefits for both types of testing:

• Speeds up processes;
• Harmonizes results;
• Facilitates integration into CI/CD pipelines.

Smoke tests are quickly automated and ideal for assessing assembly stability in continuous integration environments. For example, the 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 validate further or roll back.

Regression tests are voluminous and run more frequently, so they require automation. In large projects, manually running a full regression suite takes anywhere from a few hours to a few days. After the publication of the Capgemini World Quality Report, it became known that more than 60% of teams cite regression test automation as a key factor in accelerating release and improving product quality.

Best Practices and Recommendations

Experts from top software testing companies recommend including smoke and regression tests in your QA strategy. Here are some recommendations to help make tests more reliable and less routine for the team. They will also improve the quality of test cases.

1. Keep scripts up to date, remove obsolete tests (especially regression tests), and update expected results after the last major changes to the product.
2. The test suite should include only the most important scenarios responsible for the performance of key functions. This will speed up testing and increase its value.
3. The regression suite should not contain duplicate tests. Redundancy is bad because it increases support costs and execution time.
4. The one-test-one-result principle means that each test tests a specific functionality, while broad tests make it difficult to diagnose bugs and automate.
5. Negative scenarios in regression are needed; they test the system's behavior under erroneous inputs and incorrect actions.
6. Using metrics and performance evaluation, prioritize and refine the test suite, that is, keep track of which tests detect defects and which fail.
7. The quality of test case writing will be higher if you define goals, document prerequisites, expected results, and context. Scripts should be understandable to any team member, and the most stable ones the team automates. This saves a lot of time and human resources.

Thus, the path to high software quality is built from many small but correct steps. Using smoke testing as a first filter and regression testing for deep verification, teams create products that can be trusted. These are complementary roles in the process of ensuring product quality to reduce risks and speed up releases. A systematic approach, automation, and careful attention to checking turn complex projects into success stories.

FAQ

What is smoke testing with an example?

Smoke testing is an initial, quick review of the system's basic functionality. It allows you to make sure that the application starts and its basic functions work. Such a test is necessary before proceeding to a deeper assessment.

An example of how a smoke test is used is after updating a mobile banking application, the tester conducts a basic check to see if the application opens without errors. Can you log in using a login and password? Is the balance displayed on the main page? Does the money transfer function work? If critical failures occur, for example, the application crashes after launch or it is impossible to log in to the account, the assembly is returned to the developers for correction.

Is smoke testing a subset of regression testing?

Not quite. Although these two types of verification overlap somewhat, they have different goals. During smoke testing, specialists quickly check the most important functions to make sure that the application is ready for in-depth tests. In contrast, regression testing involves a complete system check after changes or fixes to detect new defects.

Therefore, the smoke test is more of a preparatory stage than a subtype of regression test in the direct sense.

What is the difference between regression and sanity testing?

Regression testing and sanity tests are often confused, but they are different. A regression test is a large-scale test of the entire system or parts of it after changes. Testers confirm that everything works as before. A sanity test is a quick local test of a specific part of the functionality after small changes or bug fixes. This way, testers make sure that the fix does not break other parts of the system.

It can be summarized as follows: regression is a broad coverage, and sanity is a point-by-point quick check. Both approaches are important at different stages of work on the product.

Is smoke testing part of UAT?

No, smoke testing and UAT (User Acceptance Testing) are performed at different stages and have different goals. Smoke testing is performed earlier, during the development testing stage, to ensure that the system as a whole is functional. It is a technical, basic check. UAT is performed at the final stage of the project when the product is almost ready for release. End users or customers perform it to ensure that the product meets business requirements and their expectations.

To summarize, the smoke test prepares for more in-depth tests, and the UAT is the final check before entering the market.

What is the difference between smoke testing and retesting?

Smoke testing and retesting differ in purpose and are used at different stages. Smoke tests cover a broad but shallow range of checks and are aimed at quickly checking the system's main functions after a new build. Retesting occurs after a specific error or defect is fixed and aims to confirm that a specific problem has been fixed. Retesting concerns one or more narrow scenarios related to the fixed bug.

Conclusion: Smoke review generally checks the functionality, and retesting checks the success of a specific fix.

Is smoke testing a subset of regression testing?

Figuratively speaking, smoke testing checks "Is the product alive?" and regression testing checks "Is it healthy after the cure?". The smoke test is a separate type of check and not a subset of regression verification. Although smoke tests sometimes overlap with basic regression scenarios, these are two approaches regarding purpose and depth.

‍