Unit Testing vs Functional Testing | Basic Concepts, Key Differences, Pros & Cons

Read this post to learn the unit testing vs functional testing comparison, their basic concepts, and other related info. Here we break down the benefits and problems they come with.

The primary objective of software testing is to produce high-quality products. The testing process is built upon two fundamental components: unit testing & functional testing. It is worth noting that unit testing & functional testing are not mutually exclusive, despite what the title may imply. Each type of testing plays a distinct role in the software development process. It is important to recognize that some developers consider unit tests to be redundant & time-consuming. This viewpoint has led to two contrasting camps within the developer community: those who advocate for unit testing & those who oppose it. Before we deep dive into the “unit testing vs functional testing” comparison, let's go through definitions first.

What is Unit testing?

Unit testing, also referred to as "unit" or "unit-level" testing, is a software testing approach that focuses on examining individual components within an application's code. It involves testing the smallest possible units of code, typically methods or functions, to verify their expected behavior when executed by the application. Unit tests are typically written in languages such as Swift or Objective-C, which differ from JavaScript as they lack global variables.


 This characteristic simplifies unit testing since there are no external variables for the code to access beyond its scope. Unit testing involves testing individual code segments in isolation as part of the overall software testing process. Its main objective is to ensure the accurate functioning of the tested components within an API & to validate the expected behaviors of the system under test (SUT).

What is Functional Testing

Functional testing is a testing methodology that focuses on assessing the overall functionality of an application without directly examining the underlying code. It is commonly utilized in conjunction with unit testing. The responsibility of functional testers is to ensure that all aspects of the application work harmoniously & produce expected outcomes when tested in combination. This includes validating the proper functioning of menu items upon selection or click, as well as verifying the correct handling of input fields to prevent user errors.


The primary objective of functional testing is to evaluate the overall functionality of the system. It encompasses an extensive examination of various components, including hardware, network setup, back-end databases, & user interfaces. By assessing the performance of different elements, functional testing serves as a form of integration testing to ensure the intended operation of the application.

Unit testing vs Functional testing

1. One notable distinction between unit tests & functional tests lies in their return values. When executing a unit test or any automated script, it provides a true or false outcome based on whether the expected behavior was met or not. On the other hand, functional tests, which offer a more comprehensive evaluation, always yield a true result as their primary purpose is to identify issues rather than solely confirming proper functionality.

2. This characteristic renders functional tests considerably more reliable than their component-based counterparts. Regardless of any runtime incidents or crashes that occur during the testing process, functional tests consistently pinpoint areas that require enhancement, ensuring a focused improvement before the next iteration.

3. Functional tests are written to test the functionality of your application, not its security or performance. Functional testing can be faster than unit testing because it uses an automated tool to complete most of the work for you. However, since this approach doesn't require any human intervention, it's more likely to produce false negatives than true positives—that is, if your code contains bugs but they're not caught by functional tests (for example), then other types of tests would need to be run before those issues could be fixed properly.

4. The most important difference is that unit tests are usually much faster, but functional tests can be more reliable. Functional tests are also more thorough because they test all of your code in one go. Functional testing is often done on a machine that isn't being used for development—for example, if you have a laptop at home with no other projects running on it while you're working on yours, then it makes sense to run your functional tests there instead of waiting until you get home again.

5. This means they can be run while other projects are ongoing or at any time during the day (you don't need anyone else's permission). Functional testing can also parallelize; this means there will be multiple workers running different parts of each test case simultaneously so that everything runs quickly without slowing down too much due to waiting around for each step in the process.

6. There are times when you will want to write a unit test. You might be writing an application that's small and simple, or it could be a large piece of software that has been written by several people with different skill levels and experience. Regardless of the reason for testing, there are times when you need to make sure that your code is doing what it should be doing.

Unit tests offer the advantage of being quick & straightforward to write since they focus on testing individual units in isolation. Additionally, they can be executed concurrently, allowing multiple units to be tested simultaneously, even across different machines or servers, such as an app & its associated database. Determining the ideal balance between unit & functional tests is subjective & depends on the specific project requirements.

The number of tests needed can vary, & it is essential to make informed decisions based on the project's unique needs. However, it is crucial to be cautious not to excessively rely on functional testing alone, as an overemphasis on this type of testing can negatively impact the overall quality of the application.


To conclude unit testing vs functional testing, we can state that unit testing and functional testing both play a vital role in testing your code. Unit testing is a form of software testing that focuses on individual units of code. It helps you to test the functionality of your application and make sure that each element works as it should. Functional testing, on the other hand, is used to check whether or not an entire system works properly by running through its various components in sequence.

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