Complete Guide to Software Testing Life Cycle (STLC)

Testing is a more complex and important task than it may seem at first glance. The Software Testing Life Cycle (STLC) is a comprehensive approach that ensures thorough and efficient testing of software throughout development. In this guide, you will learn what the software testing life cycle is, its components, and alternatives. We will also explain why this time-consuming and meticulous approach is an integral part of the software development process. Additionally, we will share experience in choosing STLC models, overcoming potential difficulties, and organizing testing work.

STLC as a Component of SDLC

The term "software development life cycle" (SDLC) describes the entire development process. However, it differs significantly from the software testing life cycle, or STLC. To avoid confusion, let's examine in detail how they differ and where they overlap.

Software Development Life Cycle

The software development life cycle is a way to organize all stages of product creation, from creating an MVP to expanding the product after its release. A typical SDLC includes the following stages:

Planning. At this stage, you and your research team study the target audience, form the product idea, create a business plan for app development, choose a monetization model, and find a technical partner—this could be either a co-founder or an outsourcing team if you decide to use offshore development.
Requirements Elicitation. At this stage, a software requirements document is created. Your team defines the product's functionality and assesses possible risks and constraints, creating a guide for bringing your idea to life and what the final product should look like.
Design. At this stage, UI/UX specialists work on the product interface, creating a software prototype according to the technical specification.
Development and Testing. At this stage, developers implement all necessary features and integrations, while QA specialists test the source code and the entire product to ensure smooth operation for end users.
Deployment. This is the process of releasing the software into the production environment, where it will be available to end users.
Maintenance. This is the final stage of product development. After the product goes live, all efforts are directed toward monitoring system operation, identifying and fixing bugs, implementing new functionality, and other project improvements.

Software Testing Life Cycle

The software testing life cycle (STLC) defines a set of stages for product testing. It allows checking the scalability, operability, and performance of the product. Additionally, it helps reduce the number of errors before deployment. In other words, SDLC covers all software development processes, while STLC covers only those related to software testing: forming test requirements, developing test cases, and evaluating test results.

It is important to remember that the software testing life cycle begins not after development, but during the planning and requirements gathering phase. Thus, quality management can be well-planned and structured, allowing issues to be eliminated at the initial development stage and saving resources and costs for their resolution. Similarly, the STLC does not end after product release. It continues during the maintenance phase, ensuring the software functions normally after releasing new features, fixing bugs, or changing the codebase.

Stakeholders Involved in STLC

Now let's talk about who exactly is involved in the testing process. Anyone who is in any way involved in the project or interested in its success is called a stakeholder. Stakeholders participate in various stages of software development, ensuring the quality of the software product and its alignment with business tasks and goals. And their role in defining and implementing STLC is very important.

Which specialists should be involved in software testing? The composition of stakeholders may vary depending on the structure of the software development team, but typically the following roles are involved in STLC:

Product Owner (PO) - makes key decisions and oversees resource allocation throughout the process.
Project Manager (PM) - handles project organization and execution, ensuring each step aligns with project goals.
Business Analyst (BA) - analyzes business needs, identifies problems, and forms software requirements (functional and non-functional).
Designers - work closely with developers and testers to ensure all designed elements meet project requirements and user expectations.
Developers - create the product itself, collaborate closely with the testing team, provide understanding of technical aspects of the software to other team members, and fix issues identified during testing.
Quality Assurance Team (QA) - responsible for developing and executing tests, documenting issues and test results, and ensuring the software meets requirements and quality standards.
End Users - interact with the product in real-world conditions, making their feedback and participation critical for understanding software usability and verifying that the software meets user needs.

This is a typical list of stakeholders. In some cases, additional specialists may be involved. For example, projects related to healthcare or real estate may involve legal experts. They can help prioritize specific features and verify compliance with regulatory requirements. Similarly, when developing FinTech products (which always require security specialists), it is necessary to control risks related to protecting sensitive data.

STLC Phases

STLC is divided into phases that guarantee excellent software performance. Although the specifics of the development process may influence the software testing life cycle, each project goes through the following phases:

Requirements Analysis
Test Planning
Test Case Development
Test Environment Setup
Test Execution
Defect Management
Test Cycle Closure
Test Cycle Evaluation

Let's analyze each phase: what it includes, how it works, what "pitfalls" may arise during STLC, and how to handle them to achieve the best result.

1. Requirements Analysis

The testing life cycle begins with defining key testing criteria, which coincides with the start of the Software Requirements Specification (SRS) phase in SDLC. What criteria should be set for testing? Requirements for different testing stages are typically divided into entry criteria and exit criteria.

Entry criteria include all specifications for creating the test environment. This type of criteria is based on analyzing business requirements to understand the main steps for preparing an appropriate test environment.

Exit criteria, in turn, describe what requirements must be met for a specific testing stage to be considered complete. These criteria may include the following:

Functional requirements, indicating which functions must be handled
Performance requirements, concerning how these functions are handled
Security requirements, concerning data integrity and protection against unauthorized actions
Usability requirements, reflecting the user's perspective on interface convenience, understandability, engagement, etc.

This phase helps avoid ambiguities and inconsistencies in documentation and provides a clear understanding of what needs to be tested and what the desired outcome of each testing stage is.

2. Planning

After understanding the entry and exit criteria of the testing cycle, it's time for the planning phase. At this stage, it is important to consider various aspects of testing: prepare necessary devices and tools, assemble a team of appropriately qualified specialists, estimate the scope of work, and set deadlines.

To develop a well-thought-out STLC that meets all the requirements formed in the previous phase, the following steps must be taken:

Estimate the scope of work considering the key requirements formed in the previous phase to ensure deadlines and project budget can be met.
Define testing goals. Clearly formulated goals of the testing process serve as benchmarks for evaluating software quality and effectiveness. They typically include finding defects, ensuring functionality, evaluating performance, ensuring security, and improving usability. By defining testing goals, the team can align their efforts and focus on specific areas to achieve the desired outcomes in the testing phase.
Select testing methods according to the project's specifics. For example, performance testing may not be critical for custom CRM systems with a limited and precisely known number of users (e.g., for charter airlines or small logistics companies), but it is necessary for e-commerce applications, financial or gaming applications that handle huge amounts of data and process many user actions. Here are some techniques we often use in our projects:
- Unit testing - checking a piece of the codebase after its development.
- Integration testing - ensuring all modules or application components can work together consistently.
- Functional testing - checking each function individually and in combination with others.
- Regression testing - re-testing the entire application or a subset of it to ensure it continues to work as intended after changes or updates.
Consider automation. Test automation offers many benefits, including the following:
- Faster test execution. Automation speeds up the execution of test cases and reduces overall testing time.
- Improved test coverage. Automated tests can cover a wider range of scenarios, increasing the coverage of the tested software.
- Increased reliability. Automated tests provide consistent and reliable results, minimizing the risk of human error.
- Reduced manual effort. Automation eliminates the need for manual execution of repetitive test cases, saving time and effort for QA specialists.

However, automation also has several challenges and considerations that must be taken into account:

Time and effort for initial setup. Setting up automated testing frameworks and scripts requires upfront time and resource investment.
Limited effectiveness for some types of testing. Some types of testing, such as usability testing, may be better suited for manual methods because they require human judgment and intuition.
Inefficiency for small or rapidly changing projects. For small projects or projects with frequent changes, the effort required for test automation may outweigh the benefits. In such cases, manual testing may be more flexible and cost-effective.

The decision to use automation or manual methods in STLC depends on factors such as project requirements, budget, time constraints, and the nature of the testing being performed.

In our experience, automation is not a one-size-fits-all solution for all projects. Automated tests are not the only possible choice for MVPs, but they are extremely useful after product release when the team is mainly focused on improving the product, making updates, and solving problems. In this case, test automation saves time and reduces human errors.

A combination of manual and automated testing often yields the best result.

Choosing testing tools and infrastructure. These include tools for management (Jira, TestRail, Zephyr), automated testing (Selenium, Postman, Jenkins, Travis CI, BrowserStack, Appium, JUnit, TestNG, Cucumber), performance testing (Apache JMeter, LoadRunner, Gatling), and other use cases.

3. Test Case Development

The stage of creating test cases and environment is often described as one stage in STLC, but it is better to split it into two stages because test case development and test environment setup are two independent processes with their own specifics. First, let's consider the test case development stage, or test design.

At this stage, the necessary infrastructure is created, and each test activity is defined and prioritized. This ensures accurate and relevant results and visibility for the entire development team. The following sequential steps must be performed:

Define test scenarios. Develop a list of ways and situations in which users interact with the product. This stage should involve various stakeholders, including the development lead, product owner, business analyst, end users, and QA engineers. Brainstorm with all team members to identify critical user scenarios that testers should verify.
Develop and prioritize test cases. Test cases describe specific actions, input data, and expected results needed to verify the correct functioning of the software. Develop and prioritize test scenarios according to their criticality and likelihood of occurrence.
Create test scripts. Prepare a detailed step-by-step guide for implementing test cases.

These are mandatory components of the test design stage. This stage can be adapted to your needs by using a standardized test case format, which simplifies review and execution.

4. Test Environment Setup

At the next stage, an appropriate test environment must be created. This involves recreating the product's operating environment, including hardware, software, and network configurations. The test environment may include specific devices, protocols, IP addresses, web addresses, gateways, operating system versions, and security barriers (firewalls).

It is also necessary to choose visualization tools such as Docker, Vagrant, and VirtualBox. They allow storing all necessary dependencies, configurations, and software versions for the test environment and, as a result, effortlessly reproduce the test environment on various devices and servers.

Another thing to do at this stage is smoke testing, which is a group of tests to quickly check the basic capabilities of the software. The purpose of smoke testing is to determine whether the software is stable enough to proceed with further testing. Smoke testing helps identify major errors early and avoid wasting resources on checking unstable software.

5. Test Execution

When all preparatory work is completed and testers have received a stable version of the application, the main stage of the STLC begins—test execution. This stage can be divided into the following steps:

Execute test cases using selected techniques and record all results in the test management system.
Monitor and document software defects. Defects refer to all negative test results—those that do not match the expected outcome and are considered errors or bugs.
Perform regression testing to verify that changes do not disrupt product functionality.

To optimize resources, defects can be prioritized based on their severity and impact, and root cause analysis can be conducted for critical defects.

6. Defect Reporting

After test execution, it's time for defect reporting. All negative test results recorded during testing in the defect tracking system must be reported to the development team. To make it easier for developers to fix existing defects, a defect report should be created that describes all existing errors and shortcomings and indicates the desired outcome after their resolution. After developers handle the defects, your testing team should conduct another test to determine whether the errors have been fixed.

7. Test Cycle Closure and Artifact Management

To complete the STLC, the results of previous stages must be saved and analyzed. One of the final stages—test cycle closure—includes the following steps:

Archive test artifacts. These include test cases, test data, test scripts, and test results. It is important to properly archive them for future use using version control systems (Git, SVN, or TFS), cloud storage (Google Drive, Dropbox, or OneDrive), or test management tools (Jira, HP ALM, or TestRail).
Prepare summary test reports. These reports should reflect testing activities and results, including issues encountered and their resolution. They should also briefly describe the scope of testing and provide recommendations for further testing.

8. Test Cycle Evaluation

Finally, the last stage of the software testing life cycle is evaluating test results. The information contained in the summary reports prepared in the previous stage serves as a guide for further improvements. Evaluating results involves analyzing test data and metrics to understand whether testing goals were achieved and to find out which types of defects were most common during testing.

This stage is very important for evaluating testing effectiveness and determining what requires further improvement. After the test is evaluated and all necessary fixes are made and verified, the QA team presents a test completion report to stakeholders and obtains their sign-off.

We have reviewed all stages of the software testing life cycle, their main components, tools and software needed for testing, and ways to achieve better results. Next, we will look at how different software development approaches can affect STLC.

STLC in Different Software Development Methodologies

STLC has a specific set of stages applicable to all projects. However, the ways they are implemented can vary depending on the development methodology—Agile or Waterfall. In this context, we can also refer to these methodologies as the software testing life cycle.

Let's take a closer look at two popular models—Waterfall and Agile—to understand their impact on organizing the testing cycle.

The Waterfall model involves phased development, meaning each stage occurs in a specific sequence. After a particular stage is completed, development moves to the next, and returning to the previous stage is practically impossible. This means the following for the STLC process:

Testing begins only after the development phase is complete.
Since this development model does not allow the team to make sudden changes or improvise, focus is mainly on the preparatory stages of STLC.

This model can limit flexibility due to extensive documentation and a structured approach. However, its advantage is a well-organized and documented testing process. Therefore, Waterfall is suitable for small projects with fixed requirements.

The Agile application development model is an iterative and incremental approach to software development. The entire scope of work is divided into stages, each achieved through a series of sprints. Each sprint goes through planning, execution, analysis, and error correction. Agile assumes close collaboration within the team and provides high adaptability to changes at any stage of development. Agile allows reducing development time and lowering risks.

The Agile software testing life cycle is characterized by the following:

QA engineers are involved in the development cycle from the planning stage and participate in refining requirements.
Special emphasis is placed on continuous integration, testing, and delivery.

Like the Waterfall methodology, Agile has its challenges. First, the need for close and constant communication can be a problem if you hire specialized developers without sufficient experience. Therefore, it's worth carefully weighing the advantages and risks of outsourcing. Second, flexibility often becomes a drawback for projects with high regulatory compliance requirements. Such projects may benefit from a more structured approach that the Waterfall model provides.

As you can see, the choice of software testing life cycle model is determined by the specifics of the development process. To choose the best one for your project, you need to carefully analyze the available models.

STLC vs Ad-Hoc Testing

Any project involves testing and bug fixing to some extent. However, not all teams use the software testing life cycle. At first glance, it may seem too expensive and time-consuming. This encourages teams to consider alternative testing approaches to reduce costs and effort.

As an alternative to STLC, the use of ad-hoc testing as an independent method is often mentioned. This model, also known as random or "monkey" testing, is an informal approach that involves unstructured and unplanned checks. It can be useful for finding critical defects and can be included in STLC. However, as a standalone method, it does not guarantee usability, excellent performance, or overall product quality.

Using testing methods without following STLC or choosing alternative methods may seem simpler at first. However, this can complicate development and negatively affect the software in several aspects:

Communication gaps. Poor testing structure and lack of documentation can make it difficult for some team members (managers, engineers, other QA engineers, and the product owner) to understand the details of the testing process, including what was tested, what issues were found, and what steps were taken to resolve them.
Reproducing issues. For the same reasons, reproducing errors can be difficult or even impossible after ad-hoc testing, making it hard to analyze and solve problems.
Incomplete testing. With a clear and well-defined test plan for the entire team, the percentage of unnoticed errors and failures is significantly lower. Even if you use certain types of testing, without a system, you risk missing something important.
Missed deadlines and delays. First, with ad-hoc testing, it is impossible to make an accurate estimate, unlike a planned testing process. Second, a planned STLC allows predicting and eliminating issues at early stages, saving resources for their correction. This, again, cannot be achieved with the ad-hoc method.
Cost overruns. Implementing STLC is significantly more expensive than its alternatives. However, these investments pay off by reducing or preventing critical issues that could lead to financial and reputational losses. Additionally, elements of the software testing life cycle such as test automation and continuous integration allow streamlining testing processes, saving time, and reducing software development costs in the long term.
Poor user experience. No alternative method can provide the same quality as STLC. This directly affects user experience. The more errors you find and fix before users encounter them, the greater the chance of your software's success.

As you can see, using the software development life cycle has significant advantages. That is why it is a widely spread and universally recognized practice.

It is worth noting that these advantages apply not only to in-house development teams. They are also relevant for outsourcing web development services.

Outsourcing partners who adhere to STLC can provide more effective collaboration, more efficient testing, and improved overall software quality, which positively impacts both you and your clients.

Let's demonstrate this with a real example. We have experience working with clients who initially did not consider applying STLC practices to their project—a chess simulator. The app owners believed the testing process would be simple and that QA specialists could not evaluate and test the product better than experienced chess players. At first glance, it may seem they were right not to delay.

However, critical questions regarding development and testing aspects (raised by our specialists during the planning process), along with a detailed description of the proposed evaluation criteria, ultimately convinced the client of the need for a comprehensive approach to game quality assurance.

Working with STLC allowed the team to create clear documentation, plan test cases covering all important aspects of testing and development, and eliminate possible design flaws missed in earlier development stages.

As a result, initially skeptical clients realized the undeniable advantages of using STLC. You can use consulting services to analyze your business idea and evaluate the testing process. Our experienced specialists will advise you on how the software testing life cycle can help your idea and which methods are worth using in your project.

Conclusion

The software testing life cycle (STLC) is a crucial foundation for ensuring the quality, functionality, and performance of software products. It enables comprehensive test coverage, early error detection, and effective problem resolution.

In this guide, we have covered the main components of STLC, including test requirements, test planning, test execution, defect management, and test closure. We also looked at how STLC integrates with different software development methodologies, such as Waterfall and Agile, and noted their impact on organizing the testing cycle.

Whether you are developing software in-house or outsourcing web development services, it is better to choose a software development partner that adheres to STLC principles, as this leads to improved software quality, reduced risks, and increased customer satisfaction.

If you consistently prioritize quality assurance during software development and use the information and advice provided in this guide, you can create reliable, robust, and user-oriented software solutions.