Keeping the Clock Ticking: Non-Functional Requirements

Smartphone users worldwide are expected to reach 7.7 billion by 2028. With such an enormous and growing user base, non-functional requirements like performance, security, reliability, and usability can make or break businesses.

, Principal Testing Manager, Testlio

For instance, consider a banking app used by millions. It’s not enough for it to just allow transactions (a functional requirement); it must also handle high traffic during peak hours (performance), protect sensitive financial data (security), never crash mid-transaction (reliability), and offer a smooth user experience (usability). These non-functional aspects shape user trust and long-term success.

Non-functional requirements specify the behavior of the system, focusing on parameters such as software performance, security, and reliability. This is contrasted with functional testing, which focuses on what function the software must execute.

Critical to the software development and testing cycle, they define the software’s architecture and system requirements, as well as its testing requirements and objectives.

These requirements ensure that the system works as expected in the real world and define whether the software is secure, scalable, and can support large numbers of users.

In this guide, we will discuss the fundamentals of non-functional requirements. We will also explore different testing approaches, challenges faced, and how to tackle them.

TL;DR

  • They ensure performance, scalability, and reliability.
  • Non-functional requirements define the system’s specifications and how it should act.
  • They influence architecture design and test plans.

Table of Contents

What are Non-Functional Requirements?

Consider an e-commerce website hosting a massive Black Friday sale. This sale will naturally attract a large number of users to the platform. To ensure that the application can handle such user traffic, it is essential to conduct performance and load testing on the production system. 

Performance testing evaluates the system’s response to various load conditions by analyzing speed, response time, and resource usage metrics.

For the above e-commerce app example, we will execute a performance test based on the non-functional requirements. Suppose the criteria is that the website should be able to handle 10,000 users per minute; the QA team will simulate a load test with 10,000 users.

The above scenario is an example of non-functional requirements being used for testing. Non-functional requirements specify system requirements and qualities, including requirements for the system’s performance, security, and scalability. These requirements also determine whether the application is reliable and complies with standards and regulations. 

Non-functional requirements are dissimilar to functional requirements because they deal with how the application will operate instead of what it must do. For example, functional requirements for a login module would include authentication, a password reset facility, and other features. 

In contrast, non-functional requirements can be granular and consist of a response time of fewer than 2 seconds, the capability to handle 2000 concurrent logins, etc.

functional and non-functional requirements differences

Since we now know about non-functional requirements, let’s discuss their types.

Types of Non-Functional Requirements

Non-functional requirements are specified in terms of quality attributes (performance, security, and usability), standards for compliance, user experience, risk management, etc. Testers must be familiar with these various types to develop a test strategy.

A good test strategy must include test cases for non-functional requirements for maximum test coverage.

The different types of non-functional requirements are as follows.

  • Performance requirements: They specify how the system must react to heavy user load. This involves checking metrics such as startup time, response time, latency, and the maximum number of simultaneous users the application can support.

    For example, a performance requirement for a banking application would be that it should be able to process transactions within 3 seconds, even during periods of high user traffic.

  • Reliability and availability: A system should be reliable, i.e., failures and outages are rare. This is especially important for large-scale applications running across multiple countries. Availability means that if one server fails, a backup server should replace it immediately so the oncoming user traffic is not affected. 

    For example, a client requires a cloud-based service with no downtime of more than 0.1%. This is a performance requirement for availability, meaning the application should only be down for 9 hours throughout the entire year.

  • Security requirements: These requirements guarantee that the software is secure and not vulnerable to vulnerabilities and data breaches. They also focus on ensuring the information is safe and the application is not susceptible to unauthorized access.

    For instance, an application enforces that any password must be hashed through SHA-256 encryption. In addition, the administrator login must require two-factor authentication. These are mere examples of an application’s authentication security requirements. 

  • Usability requirements: Usability makes the product intuitive and accessible. These requirements guarantee the application is easy to use and intuitive for the end-user. They are critical to improving user experience and reducing errors due to an ambiguous user interface (UI).

    An example is a usability requirement that states a banking application must provide explicit error messages rather than error codes. If a user inputs the wrong PIN, a message should pop up saying “Incorrect PIN or Try Again or Reset your PIN.” This message explains why the action failed and offers a resolution, improving the overall experience.

  • Maintainability and supportability: Large software systems should be easy to maintain and fix. The software’s code must be designed to remain easy to comprehend and simple to find and fix a bug with minimal downtime.
    For instance, if there is a minor front-end issue on the homepage of a website, the team would implement a hotfix without restarting the whole system.
  • Portability and compatibility: Today, users must access software through multiple devices. This form of non-functional requirements includes hardware, software, and platform setup requirements. They guarantee that the software will efficiently operate in different environments and operating systems.

    For instance, a portability requirement would state that an application should be functional on different operating systems, such as Windows, Linux, and MacOS. Similarly, an example of a compatibility requirement is that the application should work across different browsers, such as Chrome, Safari, and Firefox.

  • Compliance and regulatory requirements: Software must adhere to the legal, industry, and societal standards, as well as the laws and regulations of the relevant countries.

    For instance, an online retailer gathering user information must seek their permission and allow them to delete it under EU laws like GDPR.

How Non-Functional Requirements Influence QA and Software Testing

Now that we have explained various non-functional requirements in detail, we need to understand their impact on quality assurance (QA) and software testing. These requirements dictate the scope and character of different non-functional tests, such as performance testing and security testing. 

Non-functional requirements impact software testing in the following ways:

  • Define test strategies and tools: Non-functional requirements influence the choice of test strategies. They assist in identifying whether various types of testing, such as performance and security testing, are necessary. Additionally, they help determine the categories of tools used for these tests, e.g., JMeter for performance testing and OWASP ZAP for security testing.
  • Improve user experience and system reliability: Focusing on non-functional requirements helps improve the overall user experience and makes the system reliable. For example, optimizing load time 
  • Determine success criteria: Aligning system specification with non-functional requirements is essential to define success criteria. These criteria determine an application’s success and whether or not it is good enough to be released into production. 

    For instance, if an application cannot support a specific user load (performance requirements) and is not compliant with regulations, it does not meet the success criteria.

Testing Non-Functional Requirements: Methods and Approaches

Just like functional requirements, users’ non-functional needs eventually turn into testing requirements, which are mapped into test cases, including scenarios for performance testing, security testing, usability testing, etc.

Testing non-functional requirements

In each of these testing types, testers define a set of parameters to test. Let’s look at these types one by one and their testing parameters: 

Performance testing 

Performance testing is a form of non-functional testing that identifies how a system behaves under varying workload scenarios. It assists in identifying potential performance bottlenecks and enhancing them, making the application run smoothly in actual conditions. 

A few examples of performance test cases are as follows:

  1. Response time: Measure the amount of time it takes the application to reply to a request from a user. For example, the API for the log-in page-load of the application must reply in 2 seconds even with a heavy traffic load of users.
  2. Loading time: This is the time required for an application to load its web page content fully. For example, a test case for loading time would be to verify that the entire welcome page for an application loads in under 3 seconds, including media content (images, videos, etc.)
  3. Resource consumption: Measure and analyze the system’s consumption of resources (CPU, memory, etc.) when handling high user traffic, ensuring it does not reach a certain threshold. For example, the system’s combined CPU usage should not exceed 80%, even during peak hours.
  4. Throughput: It is the maximum number of transactions a system can handle in a time duration. Throughput is essential to ensure the application can function during peak user traffic. An example of a test case is that a system must handle 2500 TPM (Transactions per minute) without degradation in performance.

JMeter, LoadRunner, and BlazeMeter are the most commonly used performance testing tools. These tools simulate system load through virtual users. When a test is executed, the tool records performance metrics like the ones discussed above.

Security testing

Security testing assesses a system’s safety, identifying vulnerabilities such as data leakage, cyberattacks, and data breaches. The goal is to prevent data compromise and ensure compliance with security norms and regulations. 

Examples of security test cases include:

  1. Authentication testing: Ensure that only verified users can enter an application using two-factor authentication. Consider, if a user attempts to log in with incorrect credentials four times, that account should be locked.
  2. Authorization testing: This type of testing ensures that users can only access modules to which they are allowed access. For instance, a user should not have access to the admin page. When they attempt to visit the page, they should be presented with an access denied message.
  3. Data-encryption testing: Guarantees sensitive user data such as passwords, addresses, and bank account information are always encrypted. For example, security tests check that the passwords are stored in hash form in the database rather than in plain text.
  4. Penetration testing: This simulates real cyberattacks to identify vulnerabilities that hackers could exploit. Case in point, the cyber-security team can employ ethical hacking techniques to determine vulnerabilities and attempt to make them more secure.

Several security testing tools like Metasploit, Burp Suite, Nessus, etc, exist. Suppose security testing for an online banking app. The most important security test cases would be testing transactions and multi-factor authentication (MFA), validating data encryption, and penetration testing.

Usability testing

Usability testing identifies how simple and user-friendly the software is for the end-user. It deals with user experience, ease of accessibility, efficiency, etc. This testing is required to identify whether the application is functioning as per the end user’s expectations. 

Some major test cases for usability testing are as follows

  1. Ease of navigation: Ensure the application is easy for the end-user to navigate. For example, an e-commerce app should allow users to access the checkout section with three clicks.
  2. Responsiveness: The application UI must adapt to different screen sizes. For example, it should adjust its resolution based on the device, whether a laptop, smartphone, or tablet.
  3. Error handling: The error messages should be concise, informative, and unambiguous. For instance, if a user has entered an invalid email address on the login page, then the error message must indicate that the username or password is invalid.
  4. Accessibility: These test cases ensure the application is accessible and usable by disabled individuals. For instance, an end-user should be able to use a screen reader or shortcuts to interact with the application.

There are different tools to perform usability testing, such as User Testing, Google Lighthouse, Maze, etc. All these tools can be used to perform end-to-end usability testing of an app. 

Reliability testing

Reliability testing guarantees that the system is reliable and stable. It performs as expected under various conditions, and the users do not encounter unexpected failures. 

Some examples of test cases for reliability are as follows:

  1. System uptime and stability: System test cases such as load tests, failover tests, and long-duration tests help ascertain that the system is working and not freezing up for prolonged durations. For example, have an application running nonstop for 72 hours and confirm that there are no abrupt errors or crashes.
  2. Error recovery: These test cases specify how fast the system recovers if it fails or crashes unexpectedly. One such test would be simulating a server failure and recording the time it takes to recover.
  3. Data integrity: These test cases verify that data is not corrupted or lost in case of an unexpected failure. An example of such a test is restarting a database during transition and verifying that no data is lost.

Reliability testing can be performed through multiple tools such as Jmeter, Nagios, Chaos Monkey, etc. An example of reliability testing is testing a cloud storage service for its uptime, data integrity, and recovery time.

Compliance testing

Compliance testing identifies whether a software product complies with laws, regulations, and industry standards. This guarantees that the application is safe to use and will not encounter any legal problems in the future. 

A few examples of test cases for compliance testing are as follows:

  1. Data protection compliance: This type of compliance testing assures the application meets data protection legislation and norms. For instance, an app running in Europe must comply with the GDPR by offering a clear privacy policy and data removal upon user request.
  2. Security standards compliance: These test cases confirm that the application conforms to best security practices for securing sensitive information. For instance, a payment system should conform to PCI-DSS by encrypting credit card information.
  3. Industry-specific compliance: An app for a particular industry should also comply with its rules. For example, a healthcare application must adhere to HIPPA standards when handling patient information and data.

Multiple tools, such as ADA compliance checker and tenable.io, are available for compliance testing.

Challenges in Defining and Testing Non-Functional Requirements

Non-functional requirements are difficult to define because they depend on the amount of expected traffic, understanding security regulations, and real-world testing. 

Let’s look at these challenges in detail: 

  1. Inaccurate estimation of customer needs: Sometimes, the user needs regarding performance and usability are unclear. This happens due to the lack of proper research.

    For example, an e-commerce website might underestimate its user traffic. It expected a maximum of 2000 concurrent users but got 5000 users during peak hours.

  2. Budget constraints: Testing non-functional requirements requires additional tools and infrastructure setups, necessitating additional budgeting, which may not always be approved.

    For example, if a QA team wants to execute load testing, it would require an expensive cloud setup, which the company might not approve.

  3. Unclear compliance requirements: A software team might overlook regulatory requirements, which can cause legal issues later. 

    For example, if a networking application uses a VPN, it must comply with local laws. Otherwise, that application would be unusable in specific target geographies.

  4. Complexity of testing real-world scenarios: It is often difficult for the testing team to create a setup similar to real-world conditions. 

    For example, a streaming platform cannot test with millions of viewers simultaneously, even though such viewership is common for high-profile sports events.

Best Practices for Managing Non-Functional Requirements in QA

Now that we have discussed what kind of issues you can face while defining non-functional requirements, let’s discuss how to avoid them. The following are the best practices to follow when managing non-functional requirements in QA:

Non-functional requirements - best practices.
  1. Define clear and measurable requirements: The requirements should be clear and concise instead of vague. For example, instead of stating “The web page should load quickly”, the requirement should state:  “The page should load within 2 seconds for 90 percent of users.”
  2. Align requirements with business and user expectations: Design non-functional requirements to reflect real-world user needs. For example, a banking app should maintain 99% uptime for the convenience of end users and to meet regulatory requirements.
  3. Consider non-functional requirements in early development stages:  Define them early during the development cycle and design the application to incorporate them. For example, a video stream app should optimize buffering time from the start.
  4. Use tight testing tools: Identify and use the right testing tool for each non-functional requirement. For example, Apache Jmeter is the most suitable tool for performing distributed load testing on your application.
  5. Ensure cross-functional collaboration: These requirements affect multiple areas of the application. Therefore, testers should constantly collaborate with developers to manage these requirements. For example, the QA team should work with the DevOps team for requirements around reliability.

Conclusion

With the number of software users increasing daily, a ‘working’ system is insufficient. High-performing, secure, and easy-to-use software is a success differentiator amongst intense competition. Investing in a thorough non-functional requirement, therefore, is a strategic imperative. 

This requires precise and documented non-functional requirements and a skilled team to validate and verify them. Testlio is here to connect you with that high-skilled team. 

At Testlio, we ensure your software meets the highest non-functional quality standards by connecting you with our team of qualified and expert testers.

Our team will ensure that your software fulfills all non-functional requirements and provides the optimal user experience. Visit Testlio to learn more about how we can help you achieve your quality goals.