2.2. Common SDLC Models

1. Waterfall Model

Definition:
A linear, step-by-step model where each phase must be completed before the next begins.
Phases:

• Requirements: Gather and document all requirements
• Design: Define system architecture and design
• Development: Build the software
• Testing: QA team tests the software
• Deployment: Release to production
• Maintenance: Fix issues and make minor enhancements
  QA Role in Waterfall:
• QA is usually involved after development, making early defect prevention difficult.
• Requirements and test plans are finalized upfront.
  Pros:
• Easy to manage, well-documented
  Cons:
• Inflexible to changes, late QA involvement

The Waterfall Model is a structured software development approach where each phase must be finished before moving on to the next. This model is straightforward because it has clear sequential stages: Requirements, Design, Development, Testing, Deployment, and Maintenance. Each of these stages has specific goals, such as gathering requirements or testing the software. QA's role typically begins at the Testing phase when the software is built. Since QA comes in later, it may miss opportunities to prevent defects early in the process. This model is beneficial for projects where requirements are well understood, but it can struggle with changes and flexibility since everything is decided upfront.

Think of the Waterfall Model like building a house. First, you create a blueprint (Requirements), then you construct a frame (Design), followed by building walls and roofs (Development). After constructing the house, you inspect it for issues (Testing). Once all inspections pass, you move in (Deployment) and later address any home repairs (Maintenance). If you decide to add a room after it's built, you'd need significant changes, which reflects the inflexibility of the Waterfall approach.

2. Agile Model

Definition:
An iterative and incremental model where development is broken into sprints (usually 1–4 weeks), promoting flexibility, collaboration, and continuous delivery.
Sprint Activities:

• Sprint Planning: Define user stories and sprint goals
• Development & QA: Dev and QA work in parallel during the sprint
• Daily Stand-up: Share progress and blockers
• Sprint Review: Demonstrate completed features
• Sprint Retrospective: Reflect on what went well and what can improve
  QA Role in Agile:
• QA is involved from the beginning of each sprint
• Writes test cases alongside user stories
• Performs continuous testing (manual or automated)
• Participates in backlog grooming, reviews, and retrospectives
  Pros:
• Early and continuous QA involvement
  Cons:
• Requires high collaboration and adaptability

The Agile Model is a flexible approach to software development that breaks the project into smaller increments called sprints, which are usually 1 to 4 weeks long. This method allows teams to adapt quickly to changes and deliver parts of the product more regularly. In Agile, QA works from the beginning of the sprint. This means they create test cases as user stories are defined, allowing for continuous testing throughout the development phase. Agile emphasizes communication and collaboration within the team, enabling quicker feedback and a faster response to changes.

Imagine running a restaurant that serves different dishes daily. Each day, you prepare a new dish based on customer feedback from previous meals. This flexibility allows you to improve the menu every day and quickly adapt to customer preferences, similar to how Agile works. You review what went well, what dishes need improvement, and keep the menu evolving, just like Agile teams assess and refine their processes during sprint retrospectives.

QA Involvement in Each SDLC Phase

SDLC Phase – QA Responsibilities:

• Requirement Analysis: Review requirements for clarity, testability; identify potential gaps or risks
• Design: Review design documents; define test strategy; participate in test planning
• Development: Prepare test cases/scripts in parallel; collaborate with devs for early feedback
• Testing: Execute test cases (manual/automated); log defects; perform regression, functional tests
• Deployment: Perform sanity/smoke testing in staging/production; validate configurations
• Maintenance: Verify fixes, conduct regression tests, handle change requests.

QA involvement is crucial throughout all phases of the SDLC. During Requirement Analysis, QA ensures the requirements are clear and testable to avoid issues later on. In the Design phase, QA reviews the design documents, which helps align testing strategies with the application needs. When development begins, QA prepares test cases and collaborates with developers for early feedback, ensuring potential defects are caught quickly. In the Testing phase, QA executes various tests to check the software's functionality. After deployment, they validate the configurations to ensure everything works as intended. Finally, during Maintenance, QA verifies any fixes and manages change requests, ensuring ongoing quality.

Think of QA in software development like quality checks in a car manufacturing plant. At every stage—designing the car, building the parts, assembling the car, and even after it hits the road—there are inspections to ensure safety and performance. Just as these checks prevent faults in the car, thorough QA involvement at each stage of the SDLC helps catch problems early and maintain product quality.

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