Difference Between SDLC and STLC in Software Testing

🔍 Introduction

In the world of software engineering, two important terms often come up: SDLC (Software Development Life Cycle) and STLC (Software Testing Life Cycle). While they sound similar, their purposes are distinct yet interconnected.

• SDLC is the broader process that covers all stages of software development, from idea to deployment and maintenance.

• STLC is a subset of SDLC that focuses specifically on testing activities to ensure quality and reliability.

In simple words, SDLC is about creating software, while STLC is about validating and verifying the software. Let’s dive deeper into both and compare them in detail.

🖥️ What is Software Development Life Cycle (SDLC)?

SDLC is a step-by-step process for building software that is followed in software organizations. It defines a structured plan that helps in designing, developing, testing, deploying, and maintaining software systems.

The main goal of SDLC is to deliver high-quality software that meets client requirements within budget and timeline.

🔑 Phases of SDLC

1. Requirement Analysis

   • Gathering and analyzing client needs.

   • Example: An e-commerce site requires a cart, payment system, and order tracking.

2. Software Design

   • Creating architecture, UI/UX designs, and database schema.

   • Example: Wireframes and ER diagrams for the online store.

3. Software Build (Development)

   • Writing the actual code to implement the features.

   • Example: Developers create login, product catalog, and checkout modules.

4. Testing

   • QA team verifies the application functionality.

   • Example: Ensuring login and payments work properly.

5. Deployment

   • Delivering the software to users.

   • Example: Launching the website for customer access.

6. Maintenance

   • Fixing bugs and adding enhancements post-release.

   • Example: Adding a new payment gateway.

🧪 What is Software Testing Life Cycle (STLC)?

STLC is the systematic process of testing software to ensure it meets requirements and is defect-free. It is a more focused cycle compared to SDLC, dealing only with quality assurance and testing activities.

The main objective of STLC is to deliver bug-free, reliable, and user-friendly software.

🔑 Phases of STLC

1. Test Planning

   • Defining scope, strategy, resources, and timelines for testing.

   • Example: Deciding if testing will be manual, automated, or both.

2. Test Case Development

   • Writing test cases and preparing test data.

   • Example:

     Test Case ID: TC002
     Scenario: User login with invalid password
     Steps: Enter valid username + wrong password → Click Login
     Expected Result: Error message displayed.
     

3. Test Environment Setup

   • Preparing hardware, software, and data for testing.

   • Example: Setting up staging servers and test devices.

4. Test Execution

   • Running test cases and recording results.

   • Example: Executing test cases for login, search, and checkout.

5. Test Closure

   • Creating final reports, metrics, and lessons learned.

   • Example: Reporting total cases executed, defects found, and test coverage.

⚖️ Key Differences Between SDLC and STLC

Aspect	SDLC (Development)	STLC (Testing)
Domain	Focuses on software development	Focuses on software testing
Scope	Covers the entire life cycle of building software	Subset of SDLC, limited to testing phase
Phases	6 phases: Requirement → Design → Build → Test → Deploy → Maintain	5 phases: Planning → Case Development → Environment → Execution → Closure
Team Involved	Developers, designers, project managers	Testers, QA leads, test architects
Objective	To successfully develop working software	To ensure quality, reliability, and bug-free product
Members Needed	Larger team (developers + managers)	Smaller team (testers, QA engineers)
Execution Order	Starts before STLC, as development precedes testing	Runs in parallel but focused after dev modules are ready
End Result	A working software system	A tested, defect-free software system
Maintenance	Ongoing updates, enhancements, bug fixes	Regression testing, updating test cases & scripts

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📌 Real-Life Example

Imagine a food delivery application:

• SDLC Work: Developers design and build login, restaurant listing, order cart, and payment modules.

• STLC Work: Testers verify login with valid/invalid data, check restaurant listings, test order placement, and confirm payment security.

Both processes are interconnected: without SDLC there’s no software, and without STLC the software may not be reliable.

🎯 Summary

• SDLC (Software Development Life Cycle) is about creating software applications.

• STLC (Software Testing Life Cycle) is about testing software to ensure quality.

• SDLC has a broader scope, while STLC is a focused subset.

• Together, they ensure that software is not only developed but also thoroughly tested for usability, performance, and reliability.

👉 In short: SDLC builds the product, STLC makes sure the product works perfectly.