Smoke testing is an important software testing technique that is commonly used in the later stages of development and deployment. The goal of smoke testing is to validate the stability and basic functionality of a software build to determine if it is ready for further, more in-depth testing.
In this post, we will break down what exactly smoke testing is, why it is useful when performing smoke tests, and best practices for implementing effective smoke tests. By the end, you will have a solid understanding of this critical testing method.
What is Smoke Testing?
Smoke testing, also known as “build verification testing”, is a preliminary set of tests that validate the stability and testability of a new software build. The “smoke” reference comes from hardware testing, where new systems are powered on to see if any components emit actual smoke, indicating a broken piece of hardware.
With software, smoke tests evaluate whether the basic elements and flows of the system work and are stable enough to proceed with deeper testing. Rather than thoroughly analyzing every feature and workflow, smoke tests focus on:
- Sanity checking critical functionality – Validating that major use cases, integrations, and workflows function at a basic level without crashing.
- Verifying the build is testable – Ensuring the software can be exercised adequately for more in-depth testing. Catching blocking issues like crashes that would prevent rigorous testing.
- Assessing baseline performance – Monitoring for severe performance regressions compared to previous builds.
The goal is to quickly validate the stability and readiness of the release candidate build to continue testing. Smoke tests should be fast, broad, and shallow.
Why Perform Smoke Testing?
Conducting smoke testing provides several important benefits:
- Catch severe issues early – Major defects like crashes, connectivity issues, severe performance problems, etc. are identified right away, preventing wasted effort debugging bad builds later in the cycle.
- Get feedback on readiness quickly – Smoke test results provide rapid feedback on whether the team should proceed with testing the build or if additional work is needed first.
- Reduce risk – Running preliminary tests reduces risk by validating builds before they are distributed to additional testers or users who may find critical issues.
- Optimize testing timelines – Smoke testing the build first avoids long or deep testing on unstable builds that fail basic functionality and may need rework anyway.
- Improve release cadence – Having confidence in building stability via smoke tests allows teams to ship releases faster with less overhead.
Overall, smoke testing is an efficient way to uncover and address major issues early, optimize test timelines, and gain rapid feedback on build quality. This results in faster, lower-risk releases.
When Should You Smoke Test?
Smoke testing should be performed each time a new build is produced that is intended for release or broader testing. Common scenarios include:
- Testing nightly/CI builds – Running smoke tests on automated daily and continuous integration builds catches issues quickly before flawed builds waste developer time.
- Validating release candidates – Release candidates should always be smoke tested to ensure they meet a basic quality bar for formal user acceptance testing.
- After major code merges – Smoke tests can detect integration issues after merging significant new features or components into the main code branch.
- Testing infrastructure changes – Deploying to new environments, hardware, cloud platforms, etc. warrants smoke testing to uncover configuration issues.
- Regressing bugs/fixes – Smoke testing new builds containing bug fixes or enhancements guards against unintended side effects or regressions.
- General sanity checking – Any build intended for formal testing or release merits a quick smoke test even if no major changes occurred since the last stable build.
Frequent smoke testing provides regular assurance of build stability, maximizes test coverage, and reduces downstream waste from flawed builds. Teams should smoke tests early and often.
How to Perform Effective Smoke Tests
Conducting well-designed smoke tests takes some care and planning. Here are the best practices to implement effective, efficient smoke testing:
- Focus on critical functionality – Smoke tests should focus on the 20% of functionality that represents 80% of typical use cases. Test major workflows, key integrations, APIs, and UX flow over obscure corner cases.
- Leverage automation – Automated UI and API smoke tests execute much faster than manual testing. Automation also improves test consistency and frees up staff.
- Build regression suites – Re-running the same smoke test suite on each build improves efficiency over ad hoc tests. Expand tests over time as needed.
- Test across environments – Validate builds on all applicable environments like desktop, web, mobile, browsers, devices, and cloud platforms.
- Integrate into CI/CD pipelines – Incorporate smoke tests into automated build pipelines to get instant feedback on every change.
- Keep tests short – Individual smoke tests should generally run in a few minutes or less to keep the total suite under 30 minutes for rapid feedback.
- Have clear pass/fail criteria – Document expected test results and have defined conditions that constitute a failed smoke test.
- Let testers explore – Allow some ad hoc exploratory testing to supplement automated scripts and catch unpredictable edge cases.
- Tune over time – Continuously refine smoke tests based on usage patterns and issue data to focus on frequent pain points.
With well-designed automated tests, thorough environment coverage, quick and frequent execution, and clear pass/fail criteria, smoke testing becomes an invaluable gatekeeper of release quality.
Smoke Test Examples
Some examples of good smoke tests that validate critical system behaviors:
- Login – Verify users can log in successfully with valid and invalid credentials.
- Search – Check that keyword searches return expected results.
- Shopping cart – Browse items, add them to the cart, and simulate checkout.
- Payment processing – Test common payment types and confirmation of fake purchases.
- Core workflow – Do an end-to-end walkthrough of a main user workflow like order submission.
- Feature toggles – Enable/disable key features and check behavior changes.
- API connectivity – Call important APIs to ensure proper responses.
- Automated UI flows – Run automated test scripts that simulate user interactions.
- Links/navigation – Crawl the site to check for broken pages and links.
- Performance – Monitor page load times, network calls, and database queries for major spikes.
These types of non-exhaustive, broad sanity checks verify that the application works at a basic level before investing in deeper testing.
Smoke Test Success Criteria
Smoke tests should follow these success criteria to effectively validate builds:
- Fast execution – Tests typically complete in under 30 minutes total. Longer indicates too much depth.
- Automated – Smoke tests should be predominantly automated to enable frequent regression.
- Reliable results – Tests reliably pass on stable builds and catch real issues on flawed builds.
- Run early – Executed as one of the first tests on new builds.
- Broad coverage – Touches all major subsystems and use cases lightly.
- Environmental diversity – Runs across applicable platforms like mobile, web, and desktop.
- Easy maintenance – Straightforward to update and expand tests over time.
- Clear pass/fail standards – Formal criteria for passing vs. failing smoke test results.
- Minimal false negatives – Should rarely fail stable builds, signaling real issues.
Smoke testing produces substantial benefits for development teams when implemented with these best practices in mind. Frequent automated smoke tests act as an efficient quality gate to verify build stability and prevent downstream defects. By investing in smoke test automation and integrating earlier in-development workflows, teams can improve software quality and accelerate release cycles.
Common Smoke Testing Challenges
While extremely useful, smoke testing introduces some potential challenges that teams should be aware of:
- Flaky tests – Tests randomly pass/fail due to test instability, not actual software defects. Causes frustrating false negatives.
- Test maintenance – Smoke tests require ongoing maintenance as the application changes to keep coverage relevant.
- Incomplete coverage – Light testing leaves the potential for issues going undetected in untested parts of the system.
- Balancing depth vs. speed – Adding too many tests erodes the speed benefit while too few tests lower coverage.
- CI/CD integration – Pipelines must be designed to incorporate smoke testing stages at the appropriate points.
- Limited env support – Supporting automated smoke tests across many platforms, browsers, and devices can be challenging.
- Executing early – Smoke testing requires developers to build in time for smoke tests in their process rather than treating it as an afterthought.
With good test design principles, continuous improvement, and alignment to release processes, teams can overcome these limitations and maximize the risk reduction value of smoke testing.
FAQs About Smoke Testing
How is smoke testing different from sanity testing?
Smoke and sanity testing are often used interchangeably. Both involve quick, broad validation of application stability and basic functionality after changes. Some key differences:
- Scope – Sanity tests usually cover a subset of the key workflows validated by smoke tests.
- Speed – Sanity testing is extremely fast, often taking 5 minutes or less. Smoke tests are generally no more than 30 minutes.
- Timing – Sanity tests can be executed earlier in development before all components are integrated. Smoke tests validate the integrated build.
So in essence, sanity testing is an even faster subset of smoke testing used to assess a minimal set of critical functions. The terms are often used interchangeably.
Should I automate smoke tests?
Yes, smoke tests should absolutely be automated. The speed and frequency of smoke testing does not lend itself to manual testing. Automated UI and API smoke tests can execute the scripts 24/7 and provide instant feedback. This frees up staff for more valuable exploratory testing.
When should smoke tests occur in CI/CD?
For CI pipelines, automated smoke tests should execute after the build stage and before the deployment stage. Smoke tests validate build stability before deployment to other environments.
In CD workflows, smoke tests are also useful after deployment stages to any pre-production environment before promoting builds to production. This catches issues introduced during deployment.
How often should I smoke test?
At a minimum, every release candidate build should undergo smoke testing to qualify for formal testing or release. For more mature CI/CD workflows, automated smoke tests can run on every code commit or nightly build to provide rapid quality feedback.
- Smoke tests are a preliminary set of automated tests that validate the stability and basic functionality of new software builds.
- Conducting frequent smoke tests reduces downstream defects, provides rapid feedback on build quality, and improves release cadence.
- Effective smoke testing focuses on critical use cases, leverages automation, runs early and has clear pass/fail criteria.
- Integrating smoke testing with CI/CD and performing these sanity checks on all release-bound builds is a proven way to improve software quality.
Smoke testing serves as an efficient first line of defense against unstable, unreliable releases by catching severe issues quickly before they reach users. Teams that leverage test automation to implement continuous smoke testing can accelerate development cycles and feel confident about the quality of their software.