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A Comprehensive Guide to Functional Testing

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A study by IBM says fixing bugs after release can cost 4 to 5 times more than fixing them during testing.

That’s why functional testing is so important in software development. It checks whether the software works as it should. Each button, input, and page is tested to see if it behaves as expected.

Functional testing helps you catch problems early. It’s a simple step that saves time, money, and reputation.

In this post, we’ll understand functional software testing, its different types, and the value it brings to any software project.

What is Functional Testing?

Functional testing is a software testing type that validates application features against pre-defined functional requirements. Its main aim is to ensure that software works as intended for end-users and meets business goals.

Functional testing doesn’t focus on how code is written or works behind the scenes, but tests every feature from the end user’s perspective. Testers check each application feature against multiple valid and invalid inputs, observe the output, and compare it with the actual output.

Real-world software functional testing examples:

  • Can users successfully sign up using Gmail?
  • Is the total order value updated when a user adds a new product to the cart?
  • Does the trading app reject the trade when the user has insufficient balance in their wallet?
  • Do users receive a success message when they submit a contact form?

Each of these checks helps ensure users get what they expect, without errors or confusion.

Bonus Tip:

Instead of manually doing functional testing, teams can use the automation testing tools to speed up the process.

Common Types of Functional Testing

Different types of testing are available to check if a software feature works properly. Below are some of the most common types of functional testing.
  • Unit Testing: To perform unit testing, QA testers write small tests to check if individual pieces of the code are working. These individual code components could be a function, a method, or even a single feature.
  • Integration Testing: It verifies how different software modules or components work when they are combined.
  • Smoke Testing: Validates that the primary features of the application work properly after the release. Performing this testing guarantees that the application is stable and can undergo further testing.
  • Sanity Testing: Generally, it is performed after the smoke testing. It ensures that code changes are working as expected. For instance, if you have added the “Sign Up with Google” feature on the signup page, it only checks that particular feature.
  • Regression Testing: Regression testing helps ensure that new code changes do not affect the application’s existing functionalities.
  • Database Testing: It tests the database schema, table, etc., and ensures that the database design is accurate and reliable.
  • Beta/Usability Testing: This testing is performed by actual end-users once the application is launched in production. After that, end-users provide feedback and teams change the application features accordingly.

Functional Testing vs. Non-Functional Testing

Aspect
Functional Testing
Non-functional testing
What it checks
It verifies whether each feature and functionality of the application works correctly.
It tests the system’s performance, usability, security, and other quality attributes under different conditions.
Examples
  • Is the user able to make a payment?
  • Does the admin get an email when the user submits the contact form?
  • Does the website load within 1/2 seconds when traffic is very high?
Testing Types
  • Unit testing
  • Integration testing
  • Sanity testing
  • Regression testing
  • Black box testing
  • Database testing
  • Load testing
  • Usability testing
  • Volume testing
  • Stress testing
  • Performance testing
Test cases written by
Mostly written by QA testers.
They are written by QA testers and system designers.
Tools Used
  • Copilot4DevOps
  • Selenium
  • Cypress
  • Postman
  • JMeter
  • LoadRunner
  • Lighthouse
Scope
Test the feature of the application.
Tests the overall performance of the whole system.
Execution
It is performed during the feature development.
It is performed before launching the application when features are ready.
User Perspective
Directly tied to user actions and business logic.
Focuses more on background processes that users don’t directly see.

Why Functional Testing Matters: Key Benefits

We have explored a few forums and threads on Quora to understand what working professionals say about the importance of automation testing in DevOps. Below, we are sharing a few points with you:

  • To Launch Bug-free Software: Functional testing helps DevOps teams identify most of the bugs in the product development phase and deliver bug-free products to end users.
  • Requirements Validation: Ensures that applications meet all specified requirements and business goals. This also helps in increasing the client’s satisfaction.
  • Saves Time and Money: By detecting and fixing bugs during the development, teams can save their time and their client’s money.
  • Faster Time-to-Market: DevOps teams can integrate functional testing into the CI/CD pipeline to automate testing. This reduces the time to launch the software in the market.
  • Ensures Cross-Platform Compatibility: Functional testing helps teams to verify that the application works perfectly on different browsers and platforms.

How to Design and Write Effective Functional Test Cases

  • Test Planning: Identify various test scenarios and understand how the feature should work under different conditions. Also, set timelines and allocate resources needed for testing.
  • Design Test Cases: Next, design test cases for each feature. For each test case, write a step-by-step process and define input data and expected outcomes.
  • Set up Test Environments: Configure the software and hardware to execute test cases. Also, prepare testing frameworks and write test scripts.
  • Execute Test Cases: Next, use different tools to execute test cases and compare the test output with the desired output. Don’t forget to track and log bugs during testing.

Role of AI in Functional Testing

Artificial intelligence (AI) is making functional testing faster and more efficient. Teams are saving hundreds of hours every month by using AI functional testing tools to write test cases and analyze test results.

Tools like Copilot4DevOps, an AI assistant for requirements management within Azure DevOps, can help testers write down the test cases and test scripts using AI. It analyzes the referenced work items, like a feature, a user story, an epic, etc., and can generate test suites, test plans, integration test cases, test scripts, etc., within Azure DevOps.

Furthermore, AI can also suggest edge cases that QA testers might miss. This reduces human errors and the chances of launching the buggy application.

AI can also analyze test logs and find the root cause of bugs without any human intervention. In short, by using AI tools in functional testing, DevOps teams can boost their productivity.

If you're using Azure DevOps and want to speed up your testing process, give Copilot4DevOps a try.

Final Thoughts

Good software doesn’t just look right. It needs to work right.

Functional testing helps check that each part of the software does what it should, based on real use cases and clear inputs.

When functional testing is combined with automation and AI tools, it becomes easier to manage even in large or complex projects.

In the end, skipping testing to save time usually ends up costing more. Great software isn’t built by chance, it’s built by catching bugs before they catch you.

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