Where Testing Fits in the SDLC

Software doesn't get built in one shot. It goes through a series of phases — planning, design, coding, testing, deployment, and maintenance. This is the Software Development Lifecycle (SDLC), and understanding where testing fits into it is crucial.

The Old Way: Waterfall

In the waterfall model, each phase happens in sequence: requirements, design, implementation, testing, deployment. Testing comes near the end, after all the code is written.

The problem? If you find a fundamental design flaw during testing, you've already spent months building on a broken foundation. Fixing it is expensive, painful, and sometimes impossible within the deadline.

The Modern Way: Agile and Shift-Left

Modern teams work in short cycles (sprints, typically 1-2 weeks). Testing happens throughout the cycle, not at the end. This is called shift-left — moving testing activities earlier in the process.

In an agile team, testers are involved from day one:
- During planning: Reviewing requirements, asking "what if" questions, identifying risks
- During development: Writing test cases alongside code, pairing with developers
- During integration: Running automated tests in CI, exploratory testing on new features
- After deployment: Monitoring production, testing in production environments

The Testing Quadrants

Lisa Crispin and Janet Gregory created a useful model called the Testing Quadrants that categorizes testing activities:

	Business-Facing	Technology-Facing
Supporting the Team	Q2: Functional tests, examples, prototypes	Q1: Unit tests, component tests
Critiquing the Product	Q3: Exploratory testing, usability, UAT	Q4: Performance, security, reliability

• Q1 and Q2 (left side) support the team during development — they help build the right thing.
• Q3 and Q4 (right side) critique the finished product — they find problems before users do.

A healthy test strategy covers all four quadrants. Most teams over-invest in Q1 (unit tests) and under-invest in Q3 (exploratory testing).

Continuous Testing

In modern DevOps, testing is continuous. Tests run automatically on every commit, every merge, and every deployment. The goal is a fast feedback loop: break something, know about it in minutes, fix it before it reaches users.

This is why learning about CI/CD matters even if you're not a DevOps engineer. Your tests need to run in pipelines, and understanding how those pipelines work makes you a more effective tester.

The key takeaway: Testing isn't a phase — it's a continuous activity that starts when the first requirement is written and doesn't stop until the software is retired.