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Everything You Need to Understand About Functional Tests

Functional testing helps you validate the requirements of your software. For instance, you'll want to verify if each function or…

By Testim,

Functional testing helps you validate the requirements of your software. For instance, you’ll want to verify if each function or component of the application works as expected. You can do this with various types of testing that all fall under the functional testing umbrella. The software you develop should also meet functional specifications. For example, a user should be able to successfully add an item to their shopping cart. If the test fails, then the functional requirement is not met.

Functional testing happens when you define test cases and then validate them with test data. Every test case definition verifies whether the test output matches the expected output. It’s important to know that functional testing verifies both invalid and valid input so you can be sure you’re covering all possible scenarios.

In testing terms, we say we’re verifying both the happy path and the unhappy path. In other words, we’re testing what we expect the user to do and what we don’t expect the user to do.

Let’s say a user is limited to ordering only one item in your store. In this case, if the user wants to order more items, then the software should throw an error or display a warning notification.

In short, functional testing is an umbrella term for multiple types of testing, such as unit testing, smoke testing, and regression testing—which all contribute to verifying the functional requirements. But first of all, why are all these testing types necessary?

Why Do You Need Testing?

To begin with, testing is the best tool to assess the quality of your software. A stable codebase allows you to develop new features much faster, staying ahead of the competition. Furthermore, software testing helps you reduce your time-to-market metric.

What are some other reasons software testing matters?

  • It helps you deliver a high-quality product to increase user or customer satisfaction.
  • Well-tested code contains fewer or ideally no bugs. This contributes directly to the security of your software and to the security of user data.
  • Testing helps you find bugs early in the software development cycle.
  • It saves a lot of time and money because there’s no longer a need for “nasty” fixes later on in the cycle.

As you can probably tell, testing is an essential part of the software development cycle. Don’t wait until the last phase of your project. Testing should be a continuous effort every time your team develops a new feature.

A Definition of Functional Testing

In brief, functional testing helps you verify your software against the client’s functional requirements. But what are those? Here’s a shortlist of typical functional requirements most software applications include:

  • Validate business rules: Imagine an insurance agency that wants to make sure its business rules have been implemented correctly. If so, the software should make the right decisions each time a customer visits the site.
  • User actions related to registration and login: for example, provide the ability to reset the password in case the user lost it.
  • Historical data: This refers to the ability to retrieve previous information, such as access or change logs.
  • Authorization: This means the ability to configure different access levels and roles within the application. The access roles define who’s able to see what type of content.

Next, what are the advantages of writing functional tests?

Benefits of Writing Functional Tests

Simply put, functional testing ensures all functional requirements have been met.

As you write functional tests, you’re also validating that the failure paths work correctly. This increases the quality of the product and its security. In case something goes wrong, the client can be sure no sensitive information has been leaked.

For example, let’s say the login component fails. The system should be able to handle such failure and show an appropriate error message. If you didn’t validate this scenario, then you might end up with a piece of software that throws plain user data in case something goes wrong. Avoid this at all costs!

Last, writing these tests ensures all components and functions are working as expected. Functional testing is also concerned with testing integrations between components. In the end, you can guarantee the end user or client a fully functional and stable piece of software.

(Want to learn more? Read Testim’s blog about the test automation pyramid).

5 Types of Functional Testing

Now let’s explore five of the most interesting types of functional testing. The most obvious one on this list is unit testing.

1. Unit Testing: Validating Atomic Pieces of Code

Unit testing is concerned with validating the smallest pieces of code, also referred to as atomic testing. This type of testing tries to isolate the business logic and checks its sanity. For example, did the development team implement the logic correctly? It’s an important part of testing because the business logic often holds the most value for a company or product. Therefore, unit testing helps guarantee the quality of your business logic.

To give an example, unit testing often focuses on testing functions. Let’s say the code contains a function to convert a string that contains a number to the number format. How do you know this function returns the correct result? You can write a test that validates whether the function indeed outputs a number.

To ensure you’re testing the business logic only, it makes sense to use mocking and stubbing. These eliminate any other factors, such as database or API calls, that might influence the end result.

It can be time-consuming to write unit tests for every single piece of business logic. However, doing so contributes heavily to the quality of your code—and that’s what’s most important.

2. Component Testing: Validating a Set of Functions

Instead of vetting an atomic piece of code, component testing focuses on testing a set of functions as a whole. Basically, the testing engineer wants to validate if the component returns the expected output for a given input.

When testing components, you already pay attention to the functional requirements. Imagine you’ve developed an authorization component. From a functional point of view, the testing engineer needs to verify if the component returns the right permissions for a particular user.

Note that component testing has a broad definition. It’s not restricted to a code component. You can also consider a web page or screen to be a component.

After you complete component testing, you’ll want to validate the integrations between components. That’s why integration testing was invented.

3. Integration Testing: Validating Component Interactions

As the word suggests, integration testing helps you determine how components behave when they have to work together. This type of testing is one of the most common and effective techniques to detect new bugs. For developers, it’s not an easy task to always think on a higher level when developing a new component. Therefore, there are more opportunities for bugs to happen when components have to interact with each other.

4. Smoke Testing: Quality Assurance Testing

You perform smoke testing only when you’ve created a new build. This means that you (or the testing engineer) need to verify the build for every small release against a set of requirements. The testing engineer doesn’t need to perform full-blown testing. That’s because you or your team members have already guaranteed the quality through different types of tests, such as unit and integration tests. However, smoke testing includes testing the most important paths or components in the software build.

Smoke testing usually happens during the quality assurance (QA) phase.

Last, let’s look at regression testing and how it helps ensure the stability of your build.

5. Regression Testing: Assuring Build Stability

Regression testing helps the testing engineer find out whether new code has caused any existing functionality to break. It’s likely that a new piece of code introduced bugs in older functionality. Therefore, it’s important to perform regression testing to ensure the stability of your code for both new and old functionality.

For example, let’s say a particular function accepts one specific format of data. If you introduce a new component that accepts a new data format, then those components can’t communicate anymore. Regression testing helps you detect such problems. Integration testing should catch these types of bugs. If such a bug slips through, though, regression testing acts as a final line of testing to catch it.

Final Words on Functional Testing

Many types of functional testing exist. In addition to the ones we’ve discussed, you can also explore sanity testing, user acceptance testing, black/white box testing, and system testing. However, to guarantee the quality and stability of your code, the above five testing types are generally enough.

Unit testing helps protect the sanity of your business logic. In contrast, integration testing helps you detect tricky bugs that can pop up when components have to interact. And don’t forget that when you complete unit and integration testing, that’s like verifying that your car engine fits in your car and can start. With just those tests, you don’t know whether your car can drive down the highway. You get that information from component, smoke, and regression testing.

Let us know how your functional testing journey works out!

This post was written by Michiel Mulders. Michiel is a passionate blockchain developer who loves writing technical content. Besides that, he loves learning about marketing, UX psychology, and entrepreneurship. When he’s not writing, he’s probably enjoying a Belgian beer!

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