Functional testing explained: How to build bug-free software

Introduction

Imagine booking a cab from a ride-sharing app that assigns a driver that's an hour away; or making a purchase on an ecommerce site where the buy button doesn't work; or placing an order at your favorite restaurant through a food-delivery app, only to learn that the food was delivered to the wrong address. Frustrating, right? When software doesn’t function as expected, users are left dissastisfied, which can lead to potential loss for organizations. This is why functional testing is crucial.

Functional testing is one of the two types of software testing; a process of evaluating the software functionality to ensure it's error-free, meets the predesigned requirements, and is of high quality. Whether you're testing app login functionality, adding items to an ecommerce cart, or making transactions on a BFSI app, functional testing should be performed to ensure that the software or application functions as intended.

What is functional testing?

Software testing is divided into two types:

• Functional testing
• Non-functional testing

Functional testing verifies each function of the application to ensure it works as per the product requirements document or functional requirements document. It tests whether the software performs the intended tasks without any issues, like login authentication, data validation, cart execution, and so on. Unlike non-functional testing, which checks software performance, usability, and security, functional testing ensures that all the features behave as per the specified user requirements.

Need for functional testing

Functional testing validates software to ensure that it meets business requirements, like:

• Accurate user inputs and outputs.
• Seamless integration with other components.
• System behavior in various environments and conditions.
• Alignment with business requirements.
• Enhanced user experience.
• Fixing defects early in the development.
• Eliminating risks. Mitigating defect-costs.
• Ensuring it's bug-free before deployment.
• Overall quality, performance, and reliability.

Example of functional testing

Imagine a healthcare app that's used for doctor consultations, delivering prescriptions, lab test bookings, and access to medical records for patients across the country. Millions of patients rely on this app for their healthcare needs. What if this app fails at a critical step, like missing a prescription delivery or lab test booking, or connecting a patient with the wrong specialist?

To prevent creating confusion amongst users, all of this should be thoroughly vetted through functional testing to ensure:

• Patients can find their medical records without delays.
• The right prescription is accessible when needed.
• Lab test bookings synchronize with partner labs.
• Patients get their medicine delivered on time.
• Patients get connected with the right doctor or specialist.

Functional testing eliminates issues and ensures that the user has a seamless and hassle-free experience with the application.

Functional testing techniques

Here are some commonly used techniques in functional testing:

System tests

This simulates real-world user interactions and validates the entire system by ensuring all of its components are working together perfectly.

Example: On an ecommerce website, the tester will log in, pick an item, apply the discount code, select a payment method, and verify if the order confirmation was received.

Equivalence tests

This test divides the data into partitions called equivalence data cases and tests one condition across all partitions to check whether all of the data sets are responding in the same manner.

Example: On a login form that uses only email addresses as usernames, the tester might try valid and invalid email formats to check if errors are handled properly.

Boundary value tests

These tests are conducted to check the extreme limits of an input range, such as the number of characters in a password, file upload limits, free shipping order rules, and more.

Example: These tests check things like password length constraints (e.g., minimum 8 characters, maximum 16 characters) or free shipping rules (e.g., minimum $50 order required for free shipping).

Decision-based tests

These test different ranges of conditional statements through the decision-making logic of the app or software.

Example: When the demand is high, ride-sharing apps apply surge pricing, which needs testing in various cases, like low-demand hours, pricing changes if it's peak hours, holiday pricing changes, and more.

Ad-hoc tests

Often performed without prewritten test cases, this is an informal method to find hidden bugs in the system, such as randomly testing multiple filters in an ecommerce website or entering mis-spelled words.

Difference between functional and non-functional testing

Both functional testing and non-functional testing is important to produce quality software. Here are the primary differences between both:

What to test in functional testing

Functional testing checks whether all features satisfy the given requirements, including: 

• Functional UI testing, like buttons, forms, links, and more.
• Business logic and workflows.
• Whether the software is bug-free.
• If each feature is working well and working together as a system.
• If there's any issue with the existing product due to new features or code changes.

Functional testing process

Here are the steps involved in functional testing: 

1. Determine the scope: Develop various test scenarios, including the functionality and usability of the software.
2. Create input and output data: Input the data for the functionality to be tested as per the user requirements.
3. Execute test cases.
4. Gather the output and identify any potential problems to fix.
5. Send the feedback to the developers and resolve any problems identified.

Types of functional testing

There are various types of functional testing that ensure the software functions as intended. Some of them are: 

• Unit testing: Tests individual components or units of code.
• Integration testing: Checks if multiple components interact and work well with each other.
• Regression testing: Tests every code commit to ensure new changes are not causing issues with the existing functionality.
• Smoke testing: Tests whether the application is stable after new releases.
• System testing: Checks whether the entire system is compliant with the given requirements.
• Functional UI testing: Tests the features of the application, such as buttons, forms, and more.
• API testing: Checks API security, performance, reliability, and functionality.
• User acceptance testing: Checks if the software can handle real-time scenarios.

Why automate functional testing

Automated functional testing verifies an application’s functionality using tools and scripts. This increases the scope and depth of the testing performed, paving the way for error-free software that satisfies user requirements. Automation testing has wider test coverage, is less prone to human or manual errors, and can run repetitive test cases without much effort. Test automation can help run test cases in various environments and keep the continuous Integration/continuous deployment (CI/CD) pipelines running uninterrupted.

Benefits of automating functional testing: 

• Improved accuracy rate.
• Increased test coverage.
• Run tests on large data sets.
• Save time on repetitive tests.
• Early bug detection and improved software quality.
• Cost reduction over time.
• Enable faster time-to-market with CI/CD pipelines.
• Faster feedback loops.
• Agile and improved development.

Best practices for functional testing

To maximize the benefit of functional testing, it's important to define the scope of testing required, engage testers early, use test automation, and check errors at every stage of completion. Here are some best practices for functional testing:

• Define clear testing objectives.
• Create a testing plan.
• Engage testers early and perform continuous testing.
• Use data-driven testing.
• Choose the right test automation tool for your project or organization.
• Automate repetitive tests and tests on large data sets.
• Foster collaboration between stakeholders.

How to choose the right functional testing tool

It's important to choose the right test automation tool for optimal software quality and consistency. Here are some factors to consider:

• Test automation capabilities, such as automation scripting, low-code/no-code options, and integration with CI/CD pipelines.
• A user-friendly interface that can be used by testers with no coding experience.
• Compatibility and integration with various platforms, browsers, and devices, including CI/CD tools like Jenkins.
• Scalability, as it's supposed to handle large data sets, complex workflows, or long-term projects.
• Remote execution through a cloud-based functional testing tool.
• Detailed reports, real-time dashboards, and error-tracking features.
• AI-powered analytics that can feature patterns in feedback.
• An active support system from the company supplying the automation testing tool.

How to perform functional testing with Zoho QEngine

Zoho QEngine supports all major functional tests, including smoke testing, sanity testing, regression testing, unit testing, and more. Here's a step-by-step guide on how to perform functional testing with Zoho QEngine:

• Analyze: Identify the scope of testing and choose the right tests for optimum results.
• Plan: Create the test scenarios and write test cases according to the defined scope.
• Create: Create a structured test suite, organize test cases, and set execution order.
• Automate: Schedule automated test runs for consistent execution.
• Share: Analyze test reports and share feedback for faster error rectification.
• Implement: Update bug fixes and test cases and repeat until the desired outcome is achieved.

Conclusion

Functional testing is a crucial part of software testing that ensures the application or software works as expected, ensuring a seamless experience for users. Functional testing plays a vital role in maintaining software quality by ensuring the software meets the business requirements, integrates well with other apps, and is error-free. With the rise of complex applications and continuous development cycles, automated functional testing has become indispensable for ensuring broader test coverage, achieving faster deployment cycles and reducing human errors.