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Software testing helps teams find defects, assess software against defined quality goals, and make better-informed decisions about whether work is ready to move forward or be released. It provides evidence about what was examined—not proof that software is defect-free.
Why is software testing important?
Testing is a quality-control activity used to examine software and related work products against agreed objectives. It can reveal defects while there is still time to address them, show how well a product meets its goals at different stages of development, and give stakeholders evidence for decisions about fixes, next steps, or release readiness. The ASTQB page presenting ISTQB Foundation Level material describes testing as a cost-effective way to detect defects and evaluate a test object at different phases of the software development lifecycle.
Testing can also help teams represent users’ needs during development and provide evidence relevant to contractual or legal compliance where applicable. Those benefits depend on what was tested and the criteria used; a test result is not, by itself, proof of compliance.
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Running a test does not automatically improve the software. Testing exposes information about behavior or quality; debugging is the subsequent work of identifying and removing the defects that testing has revealed. A team may need to diagnose the cause, change code or another work product, and then test again to check the result.
What can test results tell a team?
A test result can show whether specific behavior or a quality objective was checked under stated conditions, and whether the observed result met the expected result. Across the lifecycle, that evidence can help teams decide what to fix, whether to proceed to another phase, or whether the product is ready for a release decision.
The conclusion must stay within the test’s scope. Results depend on the cases, data, environment, and behavior examined. Some defects become visible only under particular circumstances; others may not produce an observable failure in the conditions tested. Environmental conditions can also contribute to failures. Testing can reduce uncertainty and expose important problems, but it cannot establish that no defects remain.
How are software testing and quality assurance different?
Testing and quality assurance (QA) support quality, but they focus on different things. ASTQB, presenting ISTQB Foundation Level material, characterizes testing as a product-oriented, corrective approach and QA as a process-oriented, preventive approach. In practical terms, testing examines a product or work product; QA looks at the processes used to build and test it and how those processes can be improved.
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The distinction is useful because a test result can serve both purposes. A defect may need a product fix, while recurring defects or gaps in test coverage may prompt a team to review its development or testing process. Testing contributes to quality control; it is not a substitute for broader process-focused QA.
How should a team decide what to test?
Begin with the product’s intended use, risks, requirements, and acceptance criteria. A team developing a service that handles sensitive data, for example, will need to consider security risks as well as whether expected user-visible behavior works. A test plan should connect each chosen method to the quality goal or risk it is intended to examine.
ISO/IEC 25010:2023 defines a nine-characteristic quality model for software and ICT products. The IEC publication page says the model can support work across the lifecycle, including defining requirements, assessing their completeness, identifying testing objectives, setting acceptance criteria, and establishing measures. Treat it as a planning aid rather than a project-specific answer: the characteristics to prioritize depend on the product and its context.
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Which testing and verification methods can teams use?
No single method covers every kind of risk. NISTIR 8397, published by NIST in 2021 in consultation with the National Security Agency, describes a range of developer-verification techniques. It explicitly does not claim to cover the totality of software verification, so its recommendations are a useful baseline, not a mandatory, exhaustive checklist for every project.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware match| Method | What it examines | Practical fit |
|---|---|---|
| Threat modeling | Design-level security issues | Useful for considering security risks during design, before relying only on tests of running software. |
| Automated testing | Behavior encoded in repeatable checks | Useful when checks can be run consistently as code or the product changes; it only covers the cases and assertions written. |
| Static code scanning | Source code without executing the software | Can identify potential issues from code analysis; results need interpretation and follow-up. |
| Heuristic tools for hardcoded secrets | Possible secrets embedded in code | Can help flag likely hardcoded credentials or similar values for investigation. |
| Built-in checks and protections | Safeguards implemented in the software | Can provide checks at runtime or within product components; the relevant protections depend on the design and risk. |
| Black-box test cases | Externally visible behavior, without relying on internal code structure | Useful for checking behavior against requirements or expected outcomes from the user or system boundary. |
| Code-based structural test cases | Internal code structure and paths | Useful for examining code-level behavior that may not be reached by externally focused cases alone. |
| Historical test cases | Previously identified defects or failure scenarios | Can help check that known problems do not recur after changes. |
| Fuzzing | Responses to varied or unexpected inputs | Useful for probing behavior beyond a small set of hand-selected inputs. |
| Web-application scanners | Potential issues in web applications | Applicable when the product includes a web application; findings require validation. |
| Dependency review | Included libraries, packages, and services | Important because software can depend on components beyond the code written by the team. |
The table summarizes techniques NISTIR 8397 recommends considering; it does not imply that each technique is equally useful for every product. Choose based on the risk being examined, when the method fits in the lifecycle, whether it requires executing the software, the setup and human judgment involved, and which parts of the system or work product it covers. The cited guidance does not provide a quantitative head-to-head ranking of these methods’ cost or effectiveness.
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What does testing evidence not establish?
- It does not prove the software is bug-free. Tests examine selected conditions and behaviors, not every possible state.
- It does not guarantee security or compliance. Evidence from a particular technique applies to what it actually examined; broader assurance depends on the relevant risks, requirements, and assessment.
- It does not fix the problems it finds. Defect removal requires debugging or other corrective work, followed by appropriate checks.
- It does not replace process improvement. Product testing and process-oriented QA address related but different concerns.
How to interpret industry survey figures
ISTQB’s Worldwide Software Testing Practices Report for 2015–2016 reported more than 3,200 responses from 89 countries. That describes the reach of that survey, not the current global testing workforce or the prevalence of particular practices in 2026. The report listed automation, test tools, exploratory testing, and performance, usability, and security testing among its findings or trends. These are historical survey observations, not current market statistics.
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