STLC Models in Software Development

With mistakes being an inherent component of all human creations, there’s no doubt that testing has to be an inherent component of software development as well. It helps confirm a product is built in line with user-driven demands and top industry standards. There is no single approach to testing because different development teams prefer relying on their favorite and proven software testing life cycle models, each having its own pros and cons. In our post, we will take a peek at the most popular STLC models to help you spice up your testing operations and build better products.

What is the meaning of software testing life cycle (STLC)?

The software testing cycle is a set of sequential actions a testing team performs to ensure a product meets all pre-defined quality requirements. Software testing life cycle is, in turn, an integral element of a more compound software development life cycle. So, we need to differentiate these terms.

Core STLC phases

There is a traditional sequence of software testing phases that helps build an effective testing culture and create exceptional products. However, these stages are optional. Every development situation is unique, so testing must be done based on a product’s nature and the resources available.

Different STLC models may have different takes on software testing life cycle phases, but their usual sequence is as follows:

  1. Understanding initial product requirements and evaluating automation feasibility
  2. Determining testing strategy, resources, limitations, and schedule
  3. Building test cases
  4. Preparing the technical testing environment
  5. Test execution, spotting bugs
  6. Test finalizing, documenting results

Five most popular STLC models in software testing

Waterfall model

Waterfall STLC model

The first and simplest among all software testing life cycle models, Waterfall is a linear testing style where the next stage begins only after the preceding one is finalized. This approach only has one testing cycle.
The testing phase in waterfall SDLC usually follows collecting and evaluating requirements, planning tests, and designing test cases. It can not be performed simultaneously with any other step of the cycle.


  • The most simple-to-use of all STLC models in software testing
  • It is perfect for short projects with clear, stable requirements
  • Requires fewer resources


  • Does not work for lengthy projects with changing requirements
  • User demands can be considered only at the onset, with no chance to adapt them down the road
  • Moving from stage to stage is possible only after the current stage is fully finalized

Agile STLC model

Agile STLC model

As its name implies, the agile approach is dynamic and, unlike Waterfall, doesn’t stick to a rigid scheme. Testing involves multiple iterations. Testers collaborate with developers at all steps of the agile testing life cycle, sometimes by involving customers in defect spotting and introducing changes along the way after every testing iteration.


  • The agile STLC model is perfect for shorter projects
  • It keeps testing flexible and end-user-focused
  • End-users are often involved in testing at the early stages
  • Results in better quality, fast delivery, and a more satisfying user experience


  • Suitable only for companies boasting substantial relationships with their customers
  • It can be hard to predict the amount of testing work required at the onset for lengthier and more complex projects

Spiral model

Spiral STLC model

The spiral approach to STLC in testing combines linear and iteration styles, with a focus on risk assessment. An individual iteration starts from goal planning, then moves on to risk analysis, implements necessary development, and assesses the results just to repeat these four stages again and again, as the project spiral grows. Such a spiral-looking style is the most natural because it leverages learning while the project matures.


  • Perfect for complex projects, especially those risk-sensitive or on a budget
  • Mitigates risks for developers and end-users.
  • End-users are involved early, and requirement switches can be adopted effortlessly along the way


  • Requires risk assessment mastery
  • Can be an expensive and time-consuming overkill for easy and low-risk projects

V-shaped model

V-Shaped STLC model

In this style of SDLC in software testing, the development goes simultaneously with testing without stage overlaying. Before starting coding, a verification is executed to make sure that key demands in all design components are fulfilled. After coding, the validation stage with intensive testing of all components begins to guarantee the product is defectless and performs in accordance with end-user expectations.


  • This simple and time-efficient approach is perfect for short projects with distinct requirements
  • Helps spot bugs at early stages
  • Results in better quality


  • It is a rigid scheme that requires amending the test documentation if any requirement shift happens
  • Risky for complicated, longer projects prone to frequent requirement shifts

Iterative model

Iterative STLC model

In the iterative approach, development can be started with a minimal set of requirements and improved at every next iteration stage. After the current product component is coded, the team tests it to reveal risks and flaws to be corrected at later iteration stages.


  • Helps build flawless products with minimized risks
  • The involvement of end-users in every repetition stage helps get valuable feedback early, even with minimal working functionality built
  • Changes can be made at a lower cost


  • It is hard-to-manage and more resource-consuming because it is difficult to predict the number of iterations required
  • Not a good choice for shorter projects

All of the aforementioned STLC models are directly influenced by the SDLC model the project is using and can not exist outside of it. Keep in mind that it’s practically impossible to mix STLC and SDLS models and use different approaches in each at the same time.

At ABNK we mainly use the Agile STLS model as most of our projects follow the same SDLS model.

With so many testing styles already existing and with many more to pop up in the nearest future, it is vital for every testing team to choose the testing approach that best complies with their project values and ultimate end-user needs.