Software Testing Life Cycle (STLC): A Comprehensive Guide

Diana Ipacs

September 8, 2023

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Understand the critical stages of the software testing life cycle (STLC) in different methodologies and approaches.


The Software Testing Life Cycle (STLC) is a series of defined phases used in the software testing process. It outlines the systematic steps, from requirement analysis to closure, ensuring that a software product meets its specifications and quality benchmarks. Each phase of the STLC has specific goals, activities, and deliverables that aid in identifying and rectifying defects early in the development cycle.

The software testing life cycle isn't just a theoretical framework, it's a best practice guide for testers. Adherence to the STLC ensures comprehensive coverage, from understanding requirements to defect closure. This systematic approach ensures that no stone is left unturned and that software testers can deliver a high-quality product. Following the STLC can significantly enhance the efficiency and effectiveness of the testing process.

Software testing Life Cycle (STLC)

A Short History of the Software Testing Life Cycle

In the earlier days of software development, testing was often an afterthought, done quickly after coding—with little structure or methodology. However, as software systems grew in complexity, the need for a more systematic and rigorous approach to testing became evident. By the '90s, the software industry had recognized the importance of structured testing. The concept of the "software testing life cycle", or STLC, began to take shape. It was during this period that software testing started to be seen as an integral phase of the software development life cycle (SDLC), and not just an aftermath.

With the rise of agile methodologies, DevOps, and Continuous Integration/Continuous Deployment (CI/CD) pipelines in the 21st century, the STLC has been continually refined. Testing is now integral to every phase of development, from ideation to deployment, and tools for automated testing have evolved considerably. The STLC has adapted to these changes, ensuring that quality assurance remains at the forefront of software development.

 Following the STLC ensures that every software product undergoes a thorough examination to ascertain its quality and functionality.

How the STLC Can Vary Based on the Methodology Used

Software development approaches like Waterfall and Agile have distinct phases and dynamics. DevOps emphasizes the integration of development and operations with a focus on continuous delivery and automation. The software testing life cycle adapts to the rhythm of these approaches. In Waterfall, for instance, testing is a separate phase following coding, making the STLC linear. In Agile, with its iterative cycles, STLC becomes iterative too, aligning with sprints or iterations.

The agile STLC

The most commonly used form of the software testing life cycle aligns with the Agile methodology, particularly as the software development industry has seen a significant shift towards Agile practices over the last couple of decades.

While the Agile-oriented STLC is prevalent, it's essential to note that the "best" STLC often depends on the specific project, team, or organizational needs. Some projects, especially those with well-defined requirements and minimal changes, might still benefit from a Waterfall approach. However, for many modern software development environments facing evolving requirements and seeking faster release cycles, Agile and its corresponding STLC have become the go-to choice.

The Agile-oriented software testing life cycle builds upon the principles laid out by respected Agile frameworks and institutions like the Agile Alliance,, and the Scaled Agile Framework (SAFe). Here's a breakdown of the stages in an Agile-oriented STLC:

1. Requirement Analysis

At this stage, testers collaborate closely with stakeholders, product owners, and developers to understand the product requirements and user stories. Through participating in requirement gathering sessions, testers gain insights into the expected behavior of the software. This phase ensures that the testing team is aligned with development and business goals from the very beginning.

2. Test Planning

Once requirements are understood, the test team plans the testing activities. They determine the scope of testing, choose the right testing tools, allocate resources, and set timelines. Agile test plans are more dynamic than traditional ones and can adapt to changes in subsequent sprints.

3. Test Design

In this phase, testers design the test cases, test scripts, and prepare test data. The design is based on user stories and acceptance criteria from the product backlog. Using techniques like Behavior Driven Development (BDD) can help testers craft tests that closely align with user expectations.

4. Test Execution

Testers execute the designed test cases while development is ongoing or immediately after a feature is developed. Continuous feedback is provided to the development team, allowing them to make corrections in real time. This iterative execution ensures that defects are caught and rectified early.

5. Defect Reporting

If a test case fails, the defect is logged and reported back to the development team. Agile tools like JIRA or Trello often facilitate real-time collaboration and quick defect resolution. Transparent communication is maintained to ensure that defects are prioritized and addressed promptly.

6. Test Closure

Once all test cases are executed and defects are addressed, the test cycle for that iteration or sprint is closed. Testers, developers, and stakeholders participate in a retrospective to discuss what went well, what challenges were faced, and how the process can be improved for future sprints.

7. Continuous Feedback and Improvement

The idea of continuous improvement is intrinsic to Agile. Testers are not just involved in identifying software defects but also in providing feedback about processes, tools, and collaboration methods. The insights gained are used to refine and improve the software testing life cycle for subsequent iterations.

The Waterfall Model and STLC

The Waterfall model, being one of the earliest approaches to software development, follows a strict linear sequence of phases. These are usually planning, requirements gathering, system design, implementation/coding, integration, verification/testing, deployment, and maintenance.

At their core, both the Agile and Waterfall STLCs have similar phases meant to ensure software quality, such as requirement analysis, test planning, test design, test execution, defect reporting, and closure. The primary differences lie in when these phases occur, how often they occur, and the manner in which they're executed.

In Waterfall, testing phases are distinct and sequential. Testing typically begins only after the entire software has been developed.

Each testing phase in Waterfall generally happens once. There might be potential revisits if major defects are identified later in the cycle, but this is not common practice as it can be cumbersome and costly.

The Waterfall approach to the software testing life cycle is linear and rigid. Once a phase is completed and the process moves to the next phase, revisiting a previous one can be complicated and time-consuming. Changes late in the cycle can lead to significant delays and increased costs.

In essence, the Waterfall STLC is structured, sequential, and follows a top-down approach, ensuring that each phase is thoroughly completed before moving to the next. This method provides a clear roadmap but can be less flexible when changes are required late in the development or testing cycle.

DevOps and STLC

DevOps emphasizes the integration of development (Dev) and operations (Ops) with a focus on continuous delivery and automation. In essence, automation is the enabler of the DevOps philosophy. It's what allows for the rapid and consistent flow of software from development to deployment, ensuring that software can be reliably released at any time.

In this context, STLC is heavily intertwined with the development and deployment processes:

Requirement Analysis & Test Planning: In continuous integration setups, what needs testing is defined, and tests are planned as features are ideated.

Test Design: Automated test scripts are designed to align with new features.

Test Execution: With continuous integration, tests run automatically as code is integrated.

Defect Reporting & Retesting: Issues are addressed in real time, with automation ensuring immediate retesting.

Closure: With continuous deployment, features meeting quality criteria are automatically deployed.

In DevOps, STLC emphasizes automation, rapid feedback, and seamless integration with development and deployment processes.

As we’ve seen above, the software testing life cycle's structure and flow are significantly influenced by the development methodology in use. While the core principles of testing remain the same, how and when they're applied can vary widely.

STLC in Manual vs. Automated Testing

Manual Testing

In the case of manual testing, the software testing life cycle starts with requirement analysis, followed by test planning, test case design, test execution, defect reporting, and finally, closure. The emphasis here is on human judgment, intuition, and manual execution of test cases, making STLC a more hands-on and intuitive process.

Automated Testing

Automation complements the STLC; it doesn't replace it. The life cycle stages remain, but the execution varies.

For automated testing, the STLC begins similarly with requirement analysis and test planning. However, it diverges when we reach the test case design phase, which entails script writing for automated tools. Test execution involves running these scripts, and the subsequent stages are more focused on result analysis and script maintenance. Understanding the difference between these two approaches ensures that software testers can adapt their STLC processes depending on the chosen testing method.

IT teams can contribute immensely to a product's success if they provide testers with the necessary resources during test planning or if they are receptive during the defect reporting phase. Recognizing the significance of each STLC phase can pave the way for effective communication and reduced friction.

We hope you enjoyed our article on the STLC. If your company is looking for IT professionals and you are interested in IT recruitment or IT staff augmentation, please contact us and we will be happy to help you find the right person for the job.

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