Software Testing Life Cycle: 6 STLC Phases Explained

“Explain STLC” is one of the first questions in almost every manual testing interview in India, and many freshers lose marks by listing phase names without explaining what actually happens in each. The software testing life cycle (STLC) is the structured sequence of activities a QA team follows to plan, design, execute and close testing so that quality is verified in a repeatable way.

In this guide you will learn each of the six STLC phases with its activities, entry criteria, exit criteria and deliverables, see how STLC differs from SDLC, understand how it works inside Agile sprints, and get ready-to-use interview answers.

Key takeaways

• STLC has six commonly taught phases: Requirement Analysis, Test Planning, Test Case Development, Test Environment Setup, Test Execution and Test Cycle Closure.
• Entry criteria are conditions to start a phase; exit criteria are conditions to finish it.
• Each phase produces deliverables such as the test plan, test cases, RTM, defect reports and closure report.
• In Agile, the same activities happen in smaller loops inside every sprint.

What is the software testing life cycle?

The software testing life cycle is a set of defined phases that testing goes through, from understanding requirements to formally closing a test cycle. Each phase has clear goals, inputs and outputs, so the team knows when to start, what to produce and when it is done. STLC is part of the broader Software Development Life Cycle (SDLC): SDLC covers building the product, while STLC focuses on verifying and validating it.

Why does it matter? Without a defined process, testing becomes ad hoc — important requirements get missed, environments are not ready, and nobody can say with confidence whether the product is ready to release. STLC brings predictability, traceability and measurable quality.

Entry and exit criteria in simple words

Entry criteria are the prerequisites that must be met before a phase begins — for example, “requirements document is signed off” before analysis, or “build deployed and smoke test passed” before execution. Exit criteria are the conditions that must be met to complete a phase — for example, “all planned test cases executed, no open critical defects”. Teams agree on these in the test plan, and they prevent both premature starts and endless testing.

The 6 STLC phases explained

1. Requirement Analysis

The QA team studies requirements (BRD, SRS, user stories, designs) from a testing point of view, identifies testable requirements, clarifies doubts with business analysts, product owners and developers, and decides which types of testing are needed — functional, API, performance, security and so on. Automation feasibility is also assessed here.

• Entry: requirements documents or user stories available; acceptance criteria defined.
• Exit: queries resolved; testable requirements listed; automation feasibility report accepted.
• Deliverables: requirement query log, initial Requirement Traceability Matrix (RTM), automation feasibility notes.

2. Test Planning

The test lead or manager defines the test strategy: scope (in and out), approach, tools, environments, roles, schedule, effort estimates, risks and mitigation, and the entry/exit criteria for later phases. This is where you decide, for example, that regression will be automated with Selenium and API testing done in Postman.

• Entry: requirement analysis complete; RTM and feasibility notes available.
• Exit: test plan reviewed and approved by stakeholders.
• Deliverables: test plan / test strategy document, effort estimation, resource plan.

3. Test Case Development

Testers design test scenarios and detailed test cases using techniques such as equivalence partitioning, boundary value analysis, decision tables and state transition. Test data is prepared, automation scripts are written for suitable cases, and test cases are peer-reviewed. The RTM is updated so that every requirement maps to at least one test case. Our guide on how to write test cases covers this phase in detail.

• Entry: approved test plan; requirements stable enough to design tests.
• Exit: test cases and scripts reviewed and baselined; test data ready.
• Deliverables: test scenarios, test cases, automation scripts, test data, updated RTM.

4. Test Environment Setup

The environment where testing happens — servers, databases, application build, test accounts, devices, browsers and network configuration — is prepared, often by DevOps or a separate team. It can run in parallel with test case development. QA performs a smoke test to confirm the build is stable enough for detailed testing.

• Entry: environment requirements defined in the test plan; build available.
• Exit: environment ready and smoke test passed.
• Deliverables: ready environment, smoke test results, access details for the team.

5. Test Execution

Testers run test cases (manual and automated), compare actual results with expected results, log defects for failures, retest fixed defects and run regression on impacted areas. Execution status is reported daily to the team. Clear defect reports are critical here — see how to write a bug report developers can act on quickly.

• Entry: baselined test cases, ready environment, smoke test passed, test data loaded.
• Exit: planned tests executed; critical and high defects fixed or formally deferred; agreed pass percentage reached.
• Deliverables: execution results, defect reports, updated RTM with status, daily status reports.

6. Test Cycle Closure

The team evaluates the cycle against exit criteria, analyses metrics (test coverage, defect density, defect leakage, pass/fail trends), discusses lessons learned and prepares a test closure or summary report for stakeholders. Testware such as test cases, scripts and data is archived for future releases.

• Entry: test execution complete; defect status final.
• Exit: closure report signed off; testware archived.
• Deliverables: test summary/closure report, metrics, lessons-learned document.

STLC summary table

STLC vs SDLC

Software testing life cycle in Agile

In Agile teams the software testing life cycle does not disappear — it is compressed and repeated. During backlog refinement testers analyse stories (requirement analysis); in sprint planning they estimate and plan testing; while developers code, testers write scenarios and automation; builds are deployed to QA environments through CI/CD; stories are tested and bugs fixed within the sprint; and the sprint review and retrospective act as a light closure. Documentation is leaner, but the thinking behind each phase stays the same.

How to answer “Explain STLC” in an interview

Keep it to about a minute: define STLC in one line, name the six phases in order, and for two or three phases mention a concrete deliverable from your project — for example, “In test case development I wrote around 120 test cases in Jira for the checkout module and mapped them in the RTM.” Then mention how your team followed it inside sprints. Interviewers value real examples over memorised definitions. The phases also align with the test process described in the ISTQB Foundation syllabus available at istqb.org, which is useful if you are preparing for certification.

FAQs

How many phases are in the software testing life cycle?

Six phases are most commonly taught. Some organisations merge or rename them, but the activities remain similar.

What is an RTM?

A Requirement Traceability Matrix maps each requirement to its test cases and defects, ensuring nothing is left untested.

Can test environment setup run in parallel with test case development?

Yes. They are usually done in parallel to save time.

What is the difference between STLC and the defect life cycle?

STLC describes the whole testing process; the defect (bug) life cycle describes the statuses a single defect moves through, such as New, Open, Fixed, Retest and Closed.

Who prepares the test plan?

Usually the test lead or QA manager, with input from testers, developers and the product owner.

Conclusion

The software testing life cycle gives testing a clear structure: understand, plan, design, prepare, execute and close. Learn the purpose, entry and exit criteria and deliverables of each phase, connect them to your own project examples, and you will answer STLC questions confidently in any interview. Ready to put it into practice? Browse today’s QA jobs and start applying.