Whether you’re building a customer-facing website or an internal web application, functional testing is a proactive approach to identifying and solving issues. Without this crucial step in your site-building process, these issues can frustrate users, causing potential customers to leave or delaying internal workflows.

Rigorously testing every feature and function prevents problems that could negatively impact the user experience, such as broken links, malfunctioning forms, and security vulnerabilities. Read on to learn about functional testing and best practices for implementing it.

What’s functional testing?

Functional testing is a type of software testing that verifies whether a system or application works as intended. You can use functional testing to check user interfaces, application programming interfaces, databases, security features, client/server applications, and other software functionalities.

In functional testing, you create test cases based on software specifications and execute these tests to compare results with expected outcomes. This allows you to identify issues that might impact the user experience. You can address these issues to ensure the system behaves according to predefined requirements and that all features operate correctly under various conditions.

Types of functional testing

Here are a few common testing types you might use to ensure you’re publishing high-quality sites and applications:

• Unit testing. In this type, you test individual components or software application modules in isolation to ensure they function correctly. Testing each unit allows you to identify and fix bugs early.
• Sanity testing. Sanity testing is a quick check to verify whether a specific function or bug fix works as expected. You can sanity test after receiving a new build or version to ensure critical functionalities perform without diving into deeper details. For example, after fixing a bug in a content management system (CMS), sanity testing verifies that people can still create and publish new articles without issues.
• Regression testing. Regression testing checks whether new code changes impact existing functionalities. This involves running previous applications to ensure the old code still works. For example, after updating an analytics dashboard, regression testing ensures all existing data visualization tools (like graphs and charts) work properly.
• Smoke testing. This type is also called build verification testing. It’s a preliminary test to determine whether a new software build is stable enough for further testing.
• Integration testing. Integration testing checks whether an application’s different interfaces, modules, and components work together as intended. It identifies issues when integrated units interact. For example, you can test the integration between a registration module and an email notification system to ensure new users receive a welcome email.
• Usability testing. This involves examining a software’s user interface and overall experience — whether the application or website is user-friendly, navigable, and meets visitors’ needs.

Functional testing vs. nonfunctional testing

Functional testing answers the question, “Does this feature work as expected?” For example, testing your website might involve checking whether the form submission feature correctly captures and processes visitor inputs.

On the other hand, nonfunctional testing answers the question, “How well does the system perform?” It examines software components that aren’t related to specific functions but how the website or app performs under certain conditions. This includes testing for performance, scalability, security, and usability. For example, nonfunctional testing checks how well your landing page handles a high volume of concurrent visitors.

While functional testing verifies that each feature works properly, its nonfunctional counterpart ensures the software meets performance standards and provides a consistently positive user experience.

How to implement functional testing: 5 steps and best practices

Functional testing involves structured steps to ensure your website or app works correctly. Here’s a step-by-step guide with tips to implement it.

1. Determine your testing objectives

First, clearly define what you want to achieve with your testing. Understand the specific functions and features you need to test and what success looks like for each. For example, when testing a new login feature, you’ll want to ensure people can log in with their usernames and passwords without issues.

Best practices:

• Align testing with your goals. Ensure testing objectives align with overarching website goals, like checking usability to increase engagement by 20%.
• Involve stakeholders. Include product managers, developers, designers, quality assurance teams, and other relevant stakeholders to cover all touchpoints and gain multiple perspectives.

2. Develop testing scenarios

Create scenarios to outline how people will interact with your website. You can create wireframes for rough sketches and use prototyping tools to simulate real-world use. This ensures your testing is relevant and covers practical applications.

But don’t solely focus on typical user behavior — include situations that test edge cases and boundary conditions to ensure the interface handles unexpected inputs. For example, a testing scenario for the login feature might include steps like:

• Entering the correct username and password (expected)
• Entering the incorrect username and password (expected)
• Trying to log in with an unregistered email (unexpected)

3. Prepare the necessary testing data

Collect all the data required to run your test scenarios. This includes user information, sample inputs, site speed scores, and other functionality or performance-related metrics. For the login feature, you’d need a list of valid usernames and passwords — and some invalid ones — to test error handling.

Best practices:

• Diversify data. Use a diverse data set to test different scenarios and applications, including valid data, invalid data, and data that tests the system’s limitations.
• Handle data securely. Ensure any real data used in testing is anonymous. You can also use artificial data to protect user privacy and comply with data protection regulations.

4. Formulate and execute test cases

A test case is a set of actions and expected outcomes for verifying a specific function. Create test cases based on your scenarios, data, and goals to compare expectations against actual results.

For example, the login feature’s test case might involve entering a valid username and password and checking whether it successfully logs in and redirects to the individual’s profile.

Best practices:

• Conduct in-depth test cases. Write test cases with detailed steps and expected outcomes to execute functional testing more accurately.
• Prioritize test cases. Run test cases based on business impact, scope, and urgency. Conduct functional testing on high-priority cases to identify significant issues from the outset.
• Document results. Keep detailed records of test results (including screenshots and logs) for future diagnosis and reference.

5. Review, monitor, and address issues

Analyze the results after running the test cases to find errors and bugs. You can also monitor the site’s behavior mid-test to see if all functionalities work properly.

For example, if the login feature fails and testers can’t log in, note the issue, troubleshoot it, and work on developing a bug to fix it.

Best practices:

• Automate where possible, using tools powered by artificial intelligence (AI) for repetitive test cases to save time and reduce manual errors.
• Conduct a root cause analysis to understand why problems occur and how to prevent them from happening again.
• Create a continuous feedback loop between testers and developers, such as hosting regular meetings to address issues and make improvements.

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By understanding the types of functional testing and implementing best practices, you can ensure your website runs smoothly.

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