What is STLC (Software Testing Life Cycle)?

The Software Testing Life Cycle (STLC) is the sequence of phases that structure a testing effort: requirement analysis, test planning, test case design, test environment setup, test execution, and test closure, each with defined entry and exit criteria.

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IN DEPTH

In depth.

STLC gives testing the same kind of structure the SDLC gives development. The phases are: requirement analysis (understand what to test and assess testability), test planning (scope, strategy, resources, schedule), test case design (write cases and prepare test data), test environment setup (stand up the environment and smoke-test it), test execution (run cases, log defects, retest and regress), and test closure (confirm exit criteria, archive artifacts, capture metrics and lessons learned).

The important nuance, and the interview-winning one, is that each phase has entry and exit criteria, the conditions to start and to be considered done. That is what stops a team from, say, executing tests against a broken build or declaring testing complete with critical defects open.

STLC runs in parallel with the SDLC rather than only after it, in modern, shift-left teams, testing activities start as early as requirement analysis, not at the end. Reciting the phases is fine; explaining the entry/exit criteria and the shift-left overlap with development is what shows depth.

WHY IT MATTERS

Why interviewers ask about this.

STLC is a foundational interview topic, especially for QA process and lead roles. Knowing the phases plus their entry and exit criteria, and that STLC shifts left to run alongside the SDLC, signals real process understanding rather than rote memorization.

EXAMPLE

Example scenario.

A team applies STLC explicitly: test planning defines exit criteria (95% pass, zero open Critical defects), test environment setup is gated by a passing smoke test, and test closure produces a summary report with lessons learned. The entry/exit gates keep each phase honest and the release decision objective.

TIP

Interview tip.

List the phases, but do not stop there: emphasize that each has entry and exit criteria, and that STLC overlaps the SDLC (shift-left) rather than running only at the end. That combination is what separates a memorized answer from an experienced one.

FAQ

Frequently asked questions.

What are the phases of the STLC?

Requirement analysis, test planning, test case design, test environment setup, test execution, and test closure. Each phase has defined entry and exit criteria that govern when it can start and when it is complete.

What is the difference between STLC and SDLC?

The SDLC (Software Development Life Cycle) covers building the software end to end; the STLC (Software Testing Life Cycle) covers the testing activities specifically. STLC runs in parallel with the SDLC, especially in shift-left teams where testing starts at requirement analysis.