SDLC Models & Where Testing Fits

Software is not built randomly. Every organisation follows a structured approach called the Software Development Life Cycle (SDLC), which defines how an idea becomes a working product. As a tester, you must understand the SDLC model your project uses, because it decides when you receive requirements, when builds arrive, how much time you get for testing and how you communicate with developers. Interviewers frequently ask freshers to explain these models and the tester's place in them.

Phases of the SDLC

Almost every model contains the same core phases, even if it arranges them differently.

The Waterfall Model

Waterfall is the oldest and simplest model. Each phase is completed fully before the next begins, and work flows downward like a waterfall. There is little scope to go back once a phase is closed.

Where testing fits: testing is a separate phase that starts only after coding is complete. Testers may prepare test cases in parallel, but actual execution happens late.

• Advantages: simple to understand and manage, clear milestones, strong documentation.
• Disadvantages: defects are found late (and are costly), changing requirements are hard to handle, the customer sees the product only at the end.
• Suitable for: small projects with fixed, well-understood requirements, such as a simple internal payroll report.

The V-Model (Verification and Validation Model)

The V-Model is an extension of Waterfall that pairs every development phase with a corresponding testing phase. The left side of the "V" represents verification activities (planning and design), and the right side represents validation activities (actual test execution).

Business Requirements  ----------------->  Acceptance Testing (UAT)
   System Requirements  --------------->  System Testing
     High-Level Design  ------------->  Integration Testing
       Low-Level Design  ----------->  Unit Testing
                    \       Coding       /

The key benefit is that test planning starts early. When the requirement document is ready, the acceptance test plan is written immediately, so requirement gaps surface before coding begins. The weakness is the same as Waterfall: it is rigid and does not cope well with frequent changes. It is popular in regulated domains such as banking core systems, healthcare and defence, where documentation and traceability matter.

Iterative and Incremental Models

In an incremental model, the product is built and delivered in pieces. For example, a train booking app might deliver search and booking in release 1, cancellation and refunds in release 2, and meal ordering in release 3. In an iterative model, a basic version of the whole product is built first and then refined repeatedly based on feedback.

Where testing fits: each increment or iteration is tested on its own, and earlier features must be regression tested every time new code is added. This makes regression testing a regular, ongoing activity rather than a one-time event.

The Spiral model is a risk-driven variant where each loop includes planning, risk analysis, development and evaluation. It is used for large, high-risk projects but is less common in typical service-company work.

Agile: An Overview

Agile is a mindset and family of methods (Scrum, Kanban and others) that delivers working software in short cycles, usually two-week sprints. It is based on the Agile Manifesto, which values:

• Individuals and interactions over processes and tools
• Working software over comprehensive documentation
• Customer collaboration over contract negotiation
• Responding to change over following a plan

Where testing fits: everywhere. Testers are part of the same team as developers, join requirement discussions from day one, test user stories within the same sprint, and help define acceptance criteria. Testing is continuous, not a separate phase. Most Indian product companies and many service companies now follow Agile, so you are very likely to work in it. You will learn day-to-day Scrum testing practices in a later lesson.

Comparing the Models