Types of Testing in Software Engineering

If you are creating an MVP (minimum viable product) for your business, you definitely need a comprehensive quality check to ensure that it meets your business needs and exceeds your customer's expectations. 

To this end, testing mobile or web applications is an integral aspect of the SDLC (software development lifecycle) that ensures that a system functions correctly and meets quality standards before it is released into the market. This task involves identifying errors, such as bugs, missing requirements, and glitches.

So, what are the various kinds of software testing? In this article, we will explore the different types of testing in software engineering, their pros and cons and use case scenarios. 

1. Unit Testing

A unit test examines the accuracy of a smaller, independent section of application code, typically a function or method. It aims to confirm that the code operates as intended and is in line with the developer’s theoretical rationale. 

Pros 

Some of the benefits of this method include:

• Efficient bug discovery: It aids in identifying input, output, or logic-based errors within code blocks before they propagate to production. 
• Documentation: It serves as comprehensive documentation, outlining the expected behaviour of the code. Developers refer to it when modifying or refactoring code for improved performance and composition.

Cons

However, there are some instances where unit testing is less beneficial, such as: 

• Time constraints: Generating it consumes significant time, potentially extending development timelines.
• Legacy codebases: Writing tests for legacy code can be challenging and time-consuming due to its interconnected nature and data parsing requirements.

Example of Using Unit Test

In e-commerce applications, unit testing is crucial for validating the accuracy of critical functions, such as calculating total order prices. By isolating this specific functionality, developers can ensure that factors like item prices, quantities, and discounts are accurately calculated, contributing to a seamless and reliable transaction process. Additionally, this level of checks prevents errors that could potentially result in incorrect charges to customers or financial losses for the business, ultimately boosting the general user experience and trust in the platform.

2. Acceptance Testing

This QA testing technique evaluates whether a system aligns with business logic and user requirements. It ensures the application meets functional and non-functional criteria and is user-friendly, reliable, and compliant with regulations. Acceptance tests are conducted by end users or a selected group, providing invaluable insights from their daily usage perspective.

Pros 

Some of the benefits include: 

• Automated test execution: It can be automated, which saves time and effort, particularly for large or complex applications. In other words, automation tests streamline the assessment process, allowing for quicker identification of issues and faster resolution.
• Improved user satisfaction: When users actively participate in the process, they feel more invested in the product. Their involvement ensures that the final product meets their expectations, leading to higher levels of user satisfaction and acceptance.

Cons

Below are some of the cons of this technique. 

• User knowledge requirements: Effective participation requires users to have a basic understanding of the software's functionality. So, people with limited knowledge may struggle to provide meaningful feedback, potentially impacting the effectiveness of the process.
• Limited development team involvement: The development team is typically not directly involved during testing. This can lead to communication gaps and misunderstandings.

Hypothetical Example of Acceptance Test

After the development of a new online banking platform, a select group of bank customers is invited for acceptance testing. They interact with the platform to evaluate its functionality, ensuring it meets their expectations for banking operations. This involves examining the platform's user interface, assessing ease of navigation, and rigorously testing security measures to ensure compliance with industry standards. Their feedback is instrumental in fine-tuning the platform before its official launch.

3. Performance Testing

Performance testing evaluates system responsiveness and stability under specific workloads, examining speed, robustness, reliability, and application size. Its purpose is to ensure software meets expected service levels, avoiding damage to brand reputation from poorly performing applications. 

Pros

Some of the pros include: 

• Improved Customer Experience: Identifies and addresses bottlenecks for a positive experience, enhancing customer satisfaction and loyalty.
• Better Preparation: Helps organisations anticipate unexpected traffic patterns or usage changes, preparing them for future scenarios.

Cons

Some of the challenges of this quality check technique are:

• Resource-Intensive: Requires significant hardware and software resources for simulating users or transactions, making it costly and time-consuming.
• Limited Testing Scope: Focuses primarily on system performance under stress, potentially missing other types of issues. It must be supplemented with functional, regression, or other kinds of checks, which is essential.

Example of Performance Testing

An instance of performance checks involves simulating a surge in concurrent users making purchases on an e-commerce site. This assessment evaluates the website's response time, server load, and transaction processing under high-traffic conditions. By replicating peak traffic periods, such as during sales or promotions, the QA check ensures that the site maintains acceptable performance levels without experiencing delays or system failures, thereby preventing potential revenue loss.

4. Regression Testing

It verifies that changes introduced in the codebase do not inadvertently disrupt existing functionalities. This typically involves creating tests for known bugs and rerunning them after each code modification to promptly detect any reintroduction of errors.

Pros

Some of the reasons to conduct regression assessment include:

• Validating the Impact of Code Modifications: It ensures that implemented code changes do not negatively affect existing functionalities, maintaining system integrity and safety.
• Mitigate Risks Associated With Upgrades: This quality check technique minimises risks introduced by software upgrades by verifying that new code patches do not break existing functionalities.

Cons

Some of the challenges are:

• Time and Cost Requirements: Running the check with every code change can be time-consuming, potentially increasing costs due to additional server resources or manpower.
• Complexity: Managing the increasing number and complexity of tests, especially when sequential dependencies exist, may become challenging without additional QA experts.

Regression Testing Example in Practice

Suppose a software development company releasing a video editing product with core features. Before launch, a regression test with 1000 assessment cases ensures basic functionalities. After success, adding premium features necessitates new checks. One hundred new cases will be conducted to verify new features, while the 1000 old cases will ensure that existing functions remain intact.

5. Security Testing 

Security testing involves manual or automated checks conducted during the SDLC to find weaknesses that hackers could exploit, with an emphasis on addressing susceptibilities and ensuring protection from malicious attacks and unauthorised access. 

Pros

This QA technique has some advantages, which include:

• Protection from external attacks: By revealing errors during the development phase, it helps reduce the risk of attacks, especially in transactions involving users' data.
• Reduced business risk: Comprehensive safety checks safeguard user data, preserving the application's reputation and mitigating business risks.

Cons

The drawbacks include:

• Complexity: This safety QA technique is complex and demands technical skills, making it challenging to execute effectively.
• Cost: Implementing thorough safety measures in a web or mobile application can be costly due to the need for specialised tools and expertise.

Hypothetical Example of Security Testing 

One real-world instance is when a financial institution hires ethical hackers to simulate penetration testing attacks on its online banking application to identify weaknesses before malicious actors exploit them.

6. Usability Testing 

This software quality check technique involves assessing the functionality of websites, apps, or digital products by observing real users as they navigate through tasks. Typically conducted by researchers either in person or remotely, the aim is to identify areas of confusion and improve the overall user experience.

Pros

The advantages of usability testing include:

• Validate prototypes: It allows for the validation of early prototypes, helping to identify bugs and ensuring concepts are viable before substantial investments are made.
• Identify complex flow issues: It helps in pinpointing complex flow issues, such as those encountered during e-commerce checkouts, ensuring processes are intuitive for users.

Cons 

Some of the limitations of this QA check are:

• Time and cost: Conducting the assessment can be resource-intensive in terms of both time and cost. It requires investment for adjustments and improvements based on the results.
• Limited feedback: It may suffer from small sample sizes and potential bias among testers, which can alter the accuracy and comprehensiveness of the feedback received.

Example of Usability Test

When designing an e-commerce site for beauty products, usability testing could entail inviting users to navigate through the website and purchase a specific hair care item, such as shampoo or conditioner. Observing their interactions and collecting feedback throughout the process allows designers to pinpoint potential hurdles, such as confusing navigation menus or unclear product descriptions that need refining.

7. Smoke Tests

This is a preliminary testing phase performed on software builds to check for basic functionality and stability. It aims to verify that the critical features of the application are operational and that major issues preventing further checks are absent. They are typically quick and non-exhaustive, serving as a litmus test before more comprehensive evaluation stages.

Pros

Here are some of the advantages of smoke testing: 

• Early bug detection: It aids in identifying bugs in the initial phases of the QA checks, preventing them from escalating.
• Improved development workflow: Integrating it into the development pipeline promotes a culture of quality assurance and continuous improvement, fostering a more efficient and reliable development process.

Cons

Some of the drawbacks are:

• Lack of comprehensive evaluation: Due to its limited scope with a small set of test cases, it may fail to uncover critical issues beyond the surface level.
• False Sense of Security: Passing smoke tests might give a false impression of stability, leading to inadequate evaluation of deeper functionality or neglect of potential bugs not covered by the initial examination.

Hypothetical Example of Smoke Test 

In smoke testing an e-commerce platform, fundamental functionalities like user authentication, product browsing, and adding items to the cart are prioritised. Confirming the smooth operation of these core features establishes the initial quality of the build. If users can successfully log in, navigate the product catalogue without errors, and add items to their cart without issues, it suggests that the system is stable enough to proceed to more comprehensive evaluation phases.

8. Functional Testing

This is a pivotal aspect of software testing that meticulously examines a system or application's functionality. It scrutinises the system's features, capabilities, and interactions with various components, evaluating input and output mechanisms, data manipulation, user engagements, and responses under diverse scenarios.

Pros

The pros include:

• Risk mitigation: It helps mitigate the risk of releasing software with critical issues by uncovering bugs early in the development process, reducing the likelihood of costly errors in production.
• Feature verification: Ensures required features operate as intended and the system withstands unforeseen circumstances.

Cons

Limitations of functional tests include: 

• Narrow scope: It solely addresses functional requirements, necessitating additional quality checks.
• Time-consuming: Due to its detailed nature, it may prolong testing timelines, posing challenges for rapid feature validation.

Example of Functional Testing 

Suppose a banking application undergoes functional testing to ensure it meets user requirements. Evaluators may simulate various scenarios, such as depositing funds, transferring money between accounts, and checking account balances. They verify that each function performs accurately according to specifications, including error handling for insufficient funds or incorrect inputs. 

9. Software Compatibility Testing

This is a vital facet of non-functional testing that ascertains if a particular application seamlessly operates across diverse hardware, operating system (OS), and network configurations. Simply put, does it function equally well on a Samsung Galaxy A14 as it does on an iPhone 14?

Pros

The advantages are:

• Quality assurance: By rigorously assessing the software, developers can ensure that it meets the specified requirements and functions as intended, enhancing the overall quality and reliability of the product.
• Improved user satisfaction: Thorough examination helps deliver a smoother, more seamless user experience by uncovering and rectifying issues before deployment, leading to higher levels of satisfaction and engagement with the software product.

Cons

Common challenges are:

• Many development teams encounter issues in allocating adequate resources to compatibility testing, including time, budget, and access to various devices and OS versions.
• The expanding array of devices, browsers, and OS options in the market has heightened the complexity of environments, making it challenging to ensure compatibility across all variables.

Examples of Compatibility Testing

Let’s consider a scenario where a video conferencing application is evaluated to ensure it functions seamlessly across different devices, operating systems, and network conditions. This examination guarantees that users can join meetings without issues, regardless of the device or OS they use.

10. Non-Functional Testing

This QA assessment technique evaluates aspects of software beyond its functional behaviour, including usability, performance, scalability, reliability, security, and compatibility, among others. Unlike functional testing, which focuses on features, it checks the quality of the product.

Pros

Some of the benefits include: 

• Smooth user experience: Examining the system's ability to handle concurrent user loads ensures a seamless user experience even during peak usage periods.
• Improved performance and efficiency: It aids in enhancing efficiency by identifying and resolving performance bottlenecks. Also, it allows for faster feedback and iteration cycles.

Cons

Some of the challenges are: 

• Repetition with software updates: It needs to be repeated every time the software undergoes an update, which can increase testing overhead and prolong release cycles.
• Subjective interpretation: It may lack clear pass/fail criteria, interpreting results subjective and potentially leading to inconsistencies in assessment.

Example of Non-functional Testing

Again, consider an e-commerce site preparing for a sale day. The QA team estimates peak and average daily visits to simulate maximum and average loads. Ensuring the website functions smoothly under peak loads is crucial. For instance, they verify that the dashboard loads within five seconds post-login, that email notifications are sent within one minute and that several customers can log in simultaneously. 

11. Black Box Testing

This is a QA testing process that examines the external behaviour of a system without access to its internal workings or code structure. It focuses solely on performance from an end-user perspective, simulating real-world usage scenarios and evaluating how the system behaves with different inputs.

Pros

Some of its great features include: 

• Independence from internal structure: Testers don't need knowledge of the internal codebase, allowing for an unbiased assessment of the software's functionality from the user's perspective. 
• Requirement-based assessment: By aligning test scenarios with predefined criteria, examiners ensure that the application meets its intended functionality and business objectives. 

Cons

Black box testing does have several limitations that need to be considered, such as:  

• Limited code coverage: It focuses on external behaviour, which means it may not explore all possible code paths or internal logic within the software. This results in certain defects going undetected.
• Inability to check complex algorithms: Complex business logic embedded within the software may not be effectively validated because assessors do not have access to the internal code. 

Example of Black Box Testing

For instance, consider testing the login functionality of a web application. Examiners would evaluate the login page's behaviour without access to its internal code or implementation details. They would perform actions such as entering valid credentials, clicking the login button, and verifying whether the user is successfully redirected to the application's dashboard or homepage.

12. White Box Testing

White box testing examines an application's internal logic, structure, and coding. Testers gain full access, including source code and design documents, enabling thorough inspection and verification of its inner workings, infrastructure, and integrations. 

Pros

Some of the benefits are:

• Issue identification: By manually assessing web and mobile applications prior to coding, developers can refine designs based on test results, enhancing program quality.
• Feedback gathering: Early feedback on features aids programmers, QA experts, and project managers in rectifying issues before significant development progresses.

Cons

Drawbacks include: 

• Test dependency on implementation: Checks are intricately linked to the implementation, necessitating adjustments with any changes, potentially leading to false positives and obscured bugs.
• Examination complexity: It demands skilled programmers with in-depth code understanding, complicating the assessment process and increasing resource requirements.

Example of White Box Testing

When checking a banking application's authentication system, examiners with access to the source code and design documents examine the internal logic and coding of the authentication process. They create assessment cases to validate various scenarios, such as correct login, incorrect password attempts, and account lockout procedures. 

13. Grey Box Testing 

This software QA check combines elements of both black box and white box testing. Examiners have limited understanding of the internal workings of the software, typically possessing access to high-level design documents or source code. This approach allows for assessment based on understanding the system's architecture and functionality without detailed implementation knowledge. 

Pros

Below are some of the advantages:

• Enhanced test coverage: Combining perspectives from developers and evaluators results in comprehensive coverage, boosting product quality.
• Efficient resource utilisation: With access to various documents and diagrams, assessors can devise optimal test scenarios, ensuring efficient use of resources.

Cons

Despite its benefits, it has some drawbacks.

• Restricted access to internal code: A limited understanding of the system's internal structure may hinder defect root cause identification.
• Dependency on system knowledge: Examiners require substantial system knowledge to create effective evaluation cases, particularly for complex systems.

Example of Grey Box Testing

In a healthcare app, grey box testing involves examining both internal logic and user interfaces. For instance, evaluating the app's user authentication system by inputting invalid credentials while simultaneously assessing backend responses. This approach ensures the app functions securely and efficiently, vital for safeguarding sensitive patient data and maintaining regulatory compliance in the healthcare sector.

14. Stress Testing

Stress testing verifies the resilience of websites and apps, ensuring they remain functional amidst concurrent usage. These QA checks pinpoint areas for enhancement, particularly for accommodating numerous users. The objective transcends merely identifying vulnerabilities; it assesses performance at its limits.

Pros

Some advantages of stress testing include:

• Understanding system limits: It unveils issues with memory, threads, or resources that might elude detection during typical usage, allowing preemptive troubleshooting.
• Ensuring stability: It verifies that the app remains operational without crashing or freezing, even amid high data volumes or concurrent user access, averting user frustration and costly downtimes post-launch.
• Scalability: Simulating large user loads ensures responsiveness despite heavy traffic or data processing demands, ensuring system integrity.

Cons

Limitations of this QA approach are:

• Real-world scenario prediction: Accurately simulating user behaviour and load conditions poses challenges, risking inaccurate results and ineffective assessment due to load estimation discrepancies.
• False results: It may yield false positives or negatives due to unexpected variables or configuration errors, necessitating meticulous analysis to avoid erroneous decisions.

Stress Testing Example

To illustrate, stress testing a website during peak traffic hours assesses its capability to manage concurrent visits effectively. By subjecting it to a surge of users, this process evaluates whether the website can sustain performance without experiencing significant slowdowns or crashes. 

15. API Testing

Application Program Interface (API) ^[1] tests verify the behaviour and performance of an API. It involves sending requests to the server, analysing responses, and confirming their accuracy. In addition, it includes assessing security vulnerabilities, performance issues, and potential bugs. 

Pros 

Some of the benefits include:

• Validating business logic: It ensures the correctness of business logic at the API level, which is particularly crucial when handling sensitive data and ensuring compliance and security.
• Upholding business reputation: Confirming APIs perform as expected preserves the business's reputation for quality assurance, fostering trust among customers.

Cons

Challenges of API tests are:

• Dependency management: APIs often rely on external services or databases, making test environments challenging to set up and maintain.
• Test data handling: Generating and managing data can be cumbersome, especially when dealing with large datasets or complex data structures.

Example of API Testing

A bank might check its API to ensure it can correctly process a customer's request to transfer money from one account to another. In this case, the evaluation would involve sending a simulated transfer request, including details such as the sender's account information, the recipient's account information, and the amount to be transferred. The check would verify that the API accurately processes the request, deducts the specified amount from the sender's account, and credits it to the recipient's account. Additionally, it would ensure that appropriate error handling is in place for scenarios like insufficient funds or invalid account details.

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Conclusion

Software testing is a multifaceted process crucial for ensuring the functionality of an application. From the granular focus of unit tests to the holistic evaluation of acceptance testing, each type serves a specific objective in the SDLC. 

In other words, whether it's ensuring performance under pressure, verifying security measures with penetration tests, or assessing user experience through usability assessment, each type of testing in software engineering contributes to a robust and reliable application. Hence, by incorporating a diverse range of QA checks, programmers can mitigate risks, identify defects early, and ultimately deliver software that meets the highest standards of quality and user satisfaction.

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