SDLC and STLC Explained

Harry · 21 Sep 2026 · 2 views

SDLC - Software Development Life Cycle

SDLC describes how software is built: Requirement Analysis, Design, Coding, Testing, Deployment, Maintenance. Common models: Waterfall (sequential), Agile/Scrum (iterative sprints), V-Model (each dev phase has a matching test phase).

STLC - Software Testing Life Cycle

Requirement Analysis - study SRS, identify testable requirements, raise ambiguities.
Test Planning - scope, effort, schedule, entry/exit criteria in the Test Plan.
Test Case Development - write cases, prepare data, build RTM.
Environment Setup - staging servers, test data, devices/browsers.
Test Execution - run suites, log defects with evidence.
Test Closure - metrics, lessons learned, sign-off report.

Verification vs Validation

Verification - are we building the product right? Reviews, walkthroughs, static analysis (no execution).
Validation - are we building the right product? Actual execution against user needs.

Shift-Left Testing

Start testing as early as possible: review requirements, test APIs before UI exists, run unit tests on every commit. Shift-left finds the cheap bugs.

Key Points

STLC runs inside SDLC; testing is a phase and a parallel discipline.
Entry criteria start a phase, exit criteria close it.
Verification is static, validation is dynamic.

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