Difference Between Unit Testing Vs Functional Testing: Having been in the testing industry for the past few years now, one of the most common questions I get asked is a simple one: What’s the difference between unit and functional tests? It seems like such an obvious question but it turns out that there are many reasons why people get them confused. In this article, I’m going to cover the differences between these two testing types and offer some examples of each one in action.
Unit testing is defined as a method of testing an individual unit (hence the name) of the source code. A test that serves to verify the functionality of a single, cohesive unit of code is called a unit test. Unit tests are independent and typically run in seconds or minutes; if they take longer to execute, you’re likely not writing unit tests.
Unit tests should be written by developers to assert the correct operation of source code. In a perfect world, your whole application would be made up of these tiny pieces that work together seamlessly and there’d be no need for higher-level testing. Since this isn’t always the case, we sometimes have to fall back on functional testing types.
Functional testing is defined as a method of testing the functionality of a software application. Most commonly, functional tests are used to verify end-to-end scenarios or usage models. Functional tests can range from simple page load and “happy path” scenarios all the way up to full-blown acceptance criteria. Detailed requirements documents (which might include use cases, user stories, or scenarios) are often necessary to fully understand what should be tested. Functional tests can take longer than unit tests to execute and may involve the use of external dependencies.
Functional tests are typically written by business analysts, QAs, and testers to verify that the software application is functioning correctly from a usage perspective. When done well, functional testing serves as a way of validating that the intended functionality is, in fact, working.
Difference Between Unit Testing Vs Functional Testing
We are going to talk about unit testing vs functional testing. Each of these approaches has its own strengths and weaknesses. Let’s start with the definition of what is a unit test and functional test:
- Ensures the function of each individual unit of code.
- Focuses on testing a specific and small feature in isolation for maximum test coverage.
- Is used to test the software’s logic and functionality.
- Usually requires detailed descriptions of how the tests should be performed.
- Can be automated for repeatability and improved accuracy.
- Can be used to test non-UI code.
- Expected to run quickly and require less time than functional tests when implemented correctly.
- Does not cover all of the code, so it should be used in conjunction with other testing techniques (e.g., integration tests).
- Should not be solely relied upon for ensuring that the software is working correctly.
- Can be difficult to maintain and enhance over time.
- Requires a programmer’s trained eye in order to write quality tests.
- Tests if the software application or website functions properly from end to end.
- Tests the functionality of an entire application or section of code in a holistic way.
- Can cause edge cases that would not exist when testing each unit individually.
- Can validate that the application performs as expected for real-world use.
- May be impossible to automate in some cases.
- Focuses on the testing of real world scenarios.
- Strongly related to other forms of testing (e.g., usability testing).
- Can put more load on the system, which can cause performance issues if not properly tuned.
- Time is required for each build to run through all of the functional requirements.
- Involves a lot of testing and can be resource intensive to run from a business perspective.
When to use Functional Testing?
Functional testing is generally initiated once all code has been written and unit tested, due to functional requirements often being complex and more difficult to evaluate. Functional testing is also used after unit testing when a developer has some trouble getting an implementation of a method working as expected.
When to use Unit Testing?
Unit testing should be done before the software goes into production or it will soak up time that could be better spent on writing new features, fixing bugs, or improving other areas of functionality. Unit testing is also particularly useful when developing reusable code libraries since these can be reused over and over again in different projects without causing unwanted interactions with other parts of the system.