Difference Between Smoke Testing and Regression Testing in Software Testing

Testing software is crucial to ensure that you build high-quality products. As a software tester, you need to understand the differences between smoke and regression testing to test effectively.

While they both help to validate builds, they happen to have distinct purposes. For one, while smoke testing quickly verifies core functionality and stability, regression testing checks that software changes don’t introduce new bugs.

In this post, we’ll compare smoke vs regression testing in-depth covering their purposes, differences, when to use each, and examples. You will learn here how to leverage both test types for comprehensive testing and release better software faster.

Smoke Testing vs Regression Testing: Overview

First off let’s define both of these tests to have a better understanding of their purpose.

What is Smoke Testing in Software Testing?

Smoke testing is preliminary testing performed on a new software build to validate basic functionality and stability. It checks that critical components like navigation, buttons, forms, etc work without major defects.

The goal of smoke testing is to identify failures early so major issues can be fixed before further comprehensive testing. It is quick and basic, like a sanity check, and provides a go/no-go decision on whether the software is stable enough to proceed.

Smoke testing prevents wasting time and effort on elaborate testing on unstable builds.

Smoke Testing Example

Let’s look at a smoke testing example for a new e-commerce website.

The developers have created a new build with core features – user registration, login, search, and checkout.

As the tester, you will perform smoke testing as the first step after getting this initial build.

You will test major functionality like:

• Verify user is able to register on the website by providing basic details.
• Check user is able to login with valid credentials.
• Search for a product keyword and check results are displayed.
• Add a product to cart, provide shipping and payment details, and complete the checkout process.

The focus is to validate the key workflows and identify any critical defects. If major issues like broken links or crashes are found, you fail the smoke test.

If no major defects surface, the smoke testing passes. This means the core areas are stable for more comprehensive testing.

This example shows how smoke testing is done as an initial sanity check on major flows. It is quick and high-level to assess the software’s readiness for detailed testing, and helps build confidence in the quality of the new build.

What is Regression Testing in Software Testing?

Regression testing is performed to verify existing software functionality after changes like enhancements, configuration changes, or bug fixes to ensure that the changes have not introduced new bugs or impacted desired functionality.

Comprehensive regression testing is done after smoke testing passes, to test thoroughly with end-to-end scenarios. Unlike smoke testing, regression testing is in-depth and includes both manual and automated testing.

The goal is to build confidence that changes have not caused unintended side effects and ensure the software quality is intact especially when using a change-driven methodology like Agile development which is iterative and incremental.

Regression Testing Example

Let’s look at a regression testing example for a simple calculator application.

Initially, the calculator had basic functions like addition, subtraction, multiplication, and division. It passed system testing and went into production.

Now the developer has added square root and percentage functions. After smoke testing the new build, you need to begin regression testing.

You will execute test cases to verify the original arithmetic operations still work correctly. You test different combinations of numbers including negatives. Verifying the existing functionality has not broken is critical.

Next, you will test the newly added square root and percentage functions and validate that these work correctly with different values. You also need to test the integration of the new and old functions. Using combination test cases with a mix of different operators is important.

The goal is to detect any bugs due to the new changes and ensure the calculator still works as expected. Thorough regression testing is necessary to maintain software quality after changes.

This example demonstrates how important regression testing is for validating new feature functionality along with existing features.

Difference Between Regression and Smoke Testing

The major difference is that smoke testing is a quick initial test done to validate basic functionality while regression testing is an in-depth test that verifies thorough functionality after changes.

Smoke testing is done once but regression testing is executed multiple times throughout the software development lifecycle.

How to do Smoke Testing in Software Testing

Here are the key steps to perform effective smoke testing on new builds:

• First, get an understanding of the critical business scenarios and core functionality in the software.
• Identify the major areas like key workflows, UI elements, forms, reports, etc. that need to be included for smoke testing.
• Prioritize the most important features and components that will be tested.
• Define a set of test cases that cover the major components. Keep these test cases short, basic, and executable quickly.
• Ensure the test data, test environment, and tools required to run the tests are ready.
• Run the smoke tests on the new build by executing each workflow and validating expected behavior.
• If issues surface in a particular area, dig deeper with additional targeted spot checks for that module.
• Log defects immediately when failures occur. Screenshots and videos help document issues clearly.
• Once the predefined smoke test cases are executed, determine the overall result.
• If no critical defects are found, the build passes smoke testing and is accepted for further testing.
• If major failures occur, the build fails smoke testing. Failing fast saves time and effort downstream.
• Report smoke test results to stakeholders and share recommendations based on the outcome.
• Work with developers to fix failures before initiating in-depth testing.

Why is it Called Smoke Testing?

Smoke testing gets its unique name from a testing approach used in hardware manufacturing.

When new electronic circuit boards were created, engineers would power them on to see if they worked. If the circuit started emitting smoke, it would indicate the board was faulty.

This quickly detected major defects without needing detailed testing on the boards. The smoke signaled a failed test and prevented wasting time on further testing.

Similarly, in software testing, smoke tests are designed to reveal major failures early on new builds. If the software does not pass the initial smoke testing, then extensive testing is not warranted.

How to do Regression Testing in Software Testing

Here are some key steps to carry out regression testing effectively and ensure overall quality after changes:

• Start by understanding what changes were made to the software – new features, enhancements, bug fixes, etc.
• Based on changes, determine which areas of the system will be impacted and need re-testing.
• Identify relevant existing test cases and scripts that should be re-executed. Review and update them as needed.
• Develop new test cases and scripts to thoroughly test the changed functionality and its integration.
• Ensure test data is set up appropriately to execute regression tests.
• Run the regression test suites and scripts. For efficiency, maximize test automation coverage.
• For manual tests, follow defined test scenarios and validate expected behavior. Log any defects or deviations.
• Analyze results at the end of test execution. For failures, determine the root cause – are they due to the changes made or existing issues?
• Report regression testing progress, failures and pass percentage. Share detailed defect reports with developers.
• Work with developers to fix defects before proceeding to the next testing cycle.
• Rerun tests after fixes to validate that defects are resolved. Failure retests should pass now.
• Determine pass/fail criteria for regression testing exit, usually based on critical defects fixed and pass percentage achieved.
• Retest until all critical/high defects are closed and minimum pass rate achieved.

Why Regression Testing is Necessary in Software Testing

Regression testing is a crucial part of the software testing process. Here are some key reasons why investing in regression testing is necessary:

• Changes like new features, enhancements, or bug fixes can inadvertently introduce defects that break existing functionality. Comprehensive regression testing detects such issues early.
• It validates that the software works as expected after changes. Without regression testing, unwanted side effects could reach users.
• Repeated regression testing ensures new defects are not introduced repeatedly after fixes. It prevents defect leakage.
• It confirms full functionality and integration of new features added to the system.
• Regression testing maintains software quality and stability throughout the development lifecycle.
• For large complex systems, manual regression testing is difficult. Automated regression testing is needed to quickly test changes without compromising test coverage.
• Test automation and an effective regression testing process enables continuous testing and deployment with DevOps.
• Regression testing is required to comply with regulatory standards and audits in many domains like finance, healthcare, etc.
• It builds confidence in the software by ensuring any issues due to changes are detected proactively before reaching users.

Overall, regression testing is a must to deliver high-quality, reliable software efficiently as it reduces defects and technical debt in the long run.

Smoke Testing vs Regression Testing: Comparison

Now let’s do a head-to-head comparison between smoke and regression testing to highlight more key differences:

Purpose

Smoke testing quickly validates major functionality and stability to determine if a new build is ready for detailed testing. Regression testing on the other hand thoroughly verifies software behavior after changes are made to detect bugs.

Scope

Smoke testing uses a small set of core test cases to assess critical components and workflows. In contrast, regression testing uses comprehensive test cases that cover end-to-end functionality in-depth.

Execution Timeline

Smoke testing is done right after new builds or significant code changes while regression testing is executed after smoke testing passes and continues repeatedly with iterative changes.

Failures

Smoke test failures due to severe bugs require immediate fixes before further testing. Regression test failures are logged as defects and fixed in the next iteration before proceeding.

Automation

Smoke tests can be automated but are often executed manually. In contrast, automated regression testing is necessary for large systems and continuous testing.

Outcome

Smoke testing provides a go/no-go decision on testing readiness. Regression testing ensures no unintended side effects from modifications.

When to Do Smoke Testing vs Regression Testing

Understanding when to do smoke vs regression testing enables their effective use in software testing.

Smoke testing is done:

• Right after developers create a new build of the software.
• Before any detailed testing begins on a new or modified build.
• During integration testing when integrating different modules.
• After infrastructure changes like a new database or cloud migration.
• During release testing before deployment to production.

While regression testing is performed:

• After developers fix defects found during testing.
• After new features, enhancements, or changes are added to the software.
• During the active development and testing phase.
• After smoke testing passes to validate end-to-end functionality.
• After bug fixes are done to verify defect resolution.
• During final system integration testing before release.
• Continuously as part of automated testing in Agile and DevOps processes.

Bottom line, smoke testing is the starting point and regression testing follows it repeatedly to maintain quality.

Conclusion

As a software tester or developer, having a strong grasp of smoke and regression testing techniques is essential as they both play important roles in validating software builds despite having different objectives.

Effective smoke testing quickly identifies major defects in new builds. Careful regression testing thoroughly verifies functionality and detects bugs due to modifications.

Understanding when and how to leverage these two test types based on context is key to releasing high-quality, reliable software. With a layered testing strategy utilizing smoke and regression testing, you can develop better software faster.

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