Just as development follows the SDLC, testing follows its own structured process called the Software Testing Life Cycle (STLC). The STLC defines a sequence of phases, each with clear activities, conditions to start and finish, and documents to produce. Following it makes testing systematic, measurable and repeatable instead of random clicking. "Explain the STLC" is one of the most common interview questions for freshers, so learn the phases, their order and their outputs thoroughly.
Entry and Exit Criteria
Before looking at the phases, understand two terms used throughout the STLC:
- Entry criteria are the conditions that must be true before a phase can start. Example: "The test environment is ready and a stable build has been deployed" must be true before execution starts.
- Exit criteria are the conditions that must be met before a phase can be considered complete. Example: "All planned test cases are executed and there are no open critical defects."
These criteria prevent wasted effort (testing an unstable build) and premature sign-off (releasing with serious open bugs).
The Six Phases of STLC
1. Requirement Analysis
The test team studies requirement documents or user stories to understand what must be tested. Testers identify testable requirements, raise queries on unclear points, and decide which types of testing are needed (functional, performance, security and so on). An automation feasibility check may also happen here.
- Entry: requirement documents available, application architecture understood.
- Exit: queries resolved or logged, testable requirements identified and signed off.
- Deliverables: requirement query log, list of testable requirements, initial Requirement Traceability Matrix (RTM).
2. Test Planning
The test lead or manager defines the overall approach: scope, objectives, resources, schedule, tools, environments, risks and effort estimation. Roles and responsibilities are assigned.
- Entry: requirement analysis complete, scope understood.
- Exit: test plan reviewed and approved by stakeholders.
- Deliverables: test plan document, effort and cost estimation.
3. Test Case Development
Testers write test scenarios and detailed test cases, prepare test data and, where relevant, automation scripts. Test cases are reviewed by peers or leads, and the RTM is updated to map each requirement to its test cases.
- Entry: approved test plan, requirements baselined.
- Exit: test cases reviewed and approved, test data ready.
- Deliverables: test scenarios, test cases, test data, updated RTM.
4. Test Environment Setup
The environment includes servers, databases, application builds, browsers, devices, network settings and test accounts. It is usually set up by a DevOps or infrastructure team, while testers verify it. This phase often runs in parallel with test case development. Testers perform a quick smoke test to confirm the build is stable enough for detailed testing.
- Entry: environment requirements documented, test plan available.
- Exit: environment ready, smoke test passed.
- Deliverables: ready environment, smoke test results.
5. Test Execution
Testers run test cases, compare actual results with expected results and mark each case as Pass, Fail, Blocked or Not Run. Failures are logged as defects with clear steps and evidence. Fixed defects are retested, and regression testing ensures nothing else broke.
- Entry: approved test cases, ready environment, smoke test passed.
- Exit: all planned tests executed, defects logged and tracked, exit criteria from the test plan met.
- Deliverables: executed test cases with status, defect reports, updated RTM, daily status reports.
6. Test Cycle Closure
The team evaluates whether testing objectives were achieved, analyses metrics such as defect density and test coverage, documents lessons learned and archives test artefacts for future use.
- Entry: test execution complete, defect status final.
- Exit: test closure report signed off.
- Deliverables: test summary report, test closure report, test metrics, lessons learned.
STLC at a Glance
| Phase | Key activity | Main deliverable |
|---|---|---|
| Requirement Analysis | Understand and question requirements | Query log, initial RTM |
| Test Planning | Define scope, approach, schedule, resources | Test plan, estimation |
| Test Case Development | Write and review test cases and data | Test cases, test data |
| Test Environment Setup | Prepare and verify environment | Ready environment, smoke results |
| Test Execution | Run tests, log and retest defects | Execution results, defect reports |
| Test Cycle Closure | Analyse results and close | Test closure report |
A team might define test execution exit criteria as: 100% of planned test cases executed, at least 95% passed, zero open Critical or High severity defects, all Medium defects reviewed with the product owner, and payment and booking flows passing on the top five Android devices.
SDLC vs STLC
| Aspect | SDLC | STLC |
|---|---|---|
| Scope | Entire software development, from idea to maintenance | Only the testing activities |
| Goal | Build and deliver the product | Validate and verify the product's quality |
| Performed by | Business analysts, architects, developers, testers, operations | Mainly the test team |
| Relationship | The parent life cycle | Runs within and alongside the SDLC |
In Agile, the STLC does not disappear; it becomes compressed. Within a two-week sprint you still analyse the user story, plan lightly, write test cases, check the environment, execute and close, but every phase may take hours instead of weeks and several stories may be in different phases at the same time.
When explaining the STLC, name each phase and mention one deliverable for it. Interviewers look for structured answers, and naming deliverables such as the RTM, test plan and test closure report shows real understanding rather than memorisation.
