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Before I start the actual discussion, let me clear out the misinterpretation you might have from the blog's title. I'm not encouraging anyone to choose between these two software testing types as both of them have significantly unique benefits in the development process.
A lot of developers might have told you that unit testing is a wasted effort and not really useful for the software. While those developers' words may not be true, the effectiveness of unit testing has become a subject of controversy on Hacker News and Reddit.
So now, there are two factions in the developer community - unit testing haters and unit testing defenders. On the other hand, functional testing has not gone through such disputes. Developers run this test from the user's viewpoint, and everyone acknowledges its usefulness. In the end, it's the UI and functionality of the software users prioritize.
Any application or software testing aims to ensure you deliver a top-notch product to the users. Besides, you wouldn't want your software project to belong to that 66% of tech projects that partially or completely fail. Hence, my aim in this blog is to explain the key difference between unit testing and functional testing so that you can understand what to employ in your app development initiative and when. In addition, I'll also discuss how you can keep a fine balance between these two testing methods to help you develop quality apps.
Let's walk through with our checkpoints:
Let's suppose the development of software is like building a house. This analogy might not be accurate, but we can use it to understand how one testing type differs from the other in detail.
You can compare unit testing with a building inspector. His job is to inspect different internal systems of the house, such as the foundation, roof, frame, electrical, plumbing, etc. He tests every system and ensures everything is working correctly and safely.
In such a scenario, functional testing is like the owner of the house paying a visit to the construction site. The house owner wants to know how living there will feel and mostly cares about the house look, size of the rooms, interior decoration, etc.
So, the building inspector is running a unit test on the house, and from a user's perspective, the house owner is running the functional test. In other words, unit tests ensure the code is doing what the developer wishes, and functional tests ensure the developer is doing what the client wishes.
It's time to understand them in more detail.
Unit testing is extremely helpful if you want to eliminate bugs in code. It's a well-liked testing practice embraced by many organizations. As the name says, you can test each and every component. The goal is to check all the units of the code and ensure they're running as expected without any bugs.
Usually, complex apps have a handful of variables, and practical, you can't test every one of them. But if you break them into smaller units, you can reduce the development and maintenance costs.
You can also produce bug reports that will answer your questions, such as -
and many more.
Opting for a unit test of your software will serve the following purposes:
Unit testing comes with a set of advantages that can be exceptionally helpful for your app development. Have a look at them:
So, there you go, the key aspects of unit testing. Considering the software testing and quality assurance trends in 2021, the objectives and benefits of unit testing carry considerable weight in the development process and are not just a waste of time.
Now it's time to analyze functional testing. Let's explore!
If you want to evaluate the compliance of your software system against the functional needs you have determined, you must perform functional testing. It will provide you with accurate input-output verification, and thus, you can test every functionality of your app.
You can detect bugs or glitches that developers might have missed while building the app by running a functional test. So functional testing provides crucial information about the software quality and prevents potential faults so that you can fulfill your users' and business requirements.
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Developers perform functional testing types for the following objectives:
Developers well acknowledge the benefits of this software testing method. Let me present a few of them:
Although the aim of this blog is to solely deal with the key differences between these two software testing types, allow me a minute to introduce the fundamentals of integration testing in this scenario. Trust me, it'll be worth your understanding.
Let's assume you need a login page with a username and password for your web app. You can run a unit test to check if the login page is working properly and the field length of the username and password. And you can run an integration test to ensure the user reached the home page after providing correct credentials and clicking the login option.
So, how does functional testing come into this picture?
Well, it depends on the past two tests that you have conducted. Let me present some functional testing ideas for you.
In a nutshell, both unit and integration tests are the subtypes of functional tests that reestablish the importance of software maintenance. And there's just a subtle difference between these two.
Now, let's discover how unit testing will be going head-to-head with functional testing. Here's a table featuring the key differentiating factors that set these two testing methods apart from each other.
Factors | Unit Testing | Functional Testing |
---|---|---|
Purpose | Isolating each unit of code and evaluating them | Evaluating the software’s functionality from the user's viewpoint |
Technique | White box technique | Black box technique |
Focus | Isolated units or modules | Entire software |
Complexity | Developers can easily write and perform | Comparatively more complicated than unit testing |
Test Cases | Higher number of test cases than other tests | Lower number of test cases than unit and integration |
Covered issue | Code errors and edge cases | Software performance and functionality |
Written by | Developers | Testers |
Programming language | Usually needs the same programming language | No need for the same programming language |
Change rate | Frequently changing | Not much changing |
Cost and maintenance | Low | High |
Test coverage | Number of code lines | Number of requirements |
Automation | Automation is a must | Both automation and manual test |
When to perform | At the beginning of the development process | After developers build the features |
Popular tools | NUnit, JUnit, TestNG, Mockito | UFT, Selenium, SahiPro |
Now, I will explain each factor in more detail to help you understand the importance of software testing and the contrast between these testing types.
Unit tests make up a solid foundation, and you should build the rest of the testing process on it. Developers can easily create such tests with minimal cost. Because of the huge volume of unit tests, developers generally use certain testing tools to automate the tests based on the framework or coding language.
With this test, you can verify the functionality of the smallest modules of an API in isolation. Apart from ensuring that the system under test (SUT) generates accurate results, unit testing also verifies distinct behavioral aspects of the SUT.
So, the purpose of unit testing is to help developers build a powerful codebase with low cost and provide information for high-end tests like functional and integration tests.
With functional testing types, you can test the functionality of the entire software, from its networking architecture to hardware, back-end databases, front-end UI, and so on. So, we can say that functional and integration testing are quite similar as both of them ensure the proper working of the components.
Let me explain this in simpler words. While unit testing informs you what you should fix in the codebase and where, functional testing just informs something you should fix. It could mean a race condition, the browser, or the test.
Talking about the testing techniques, let me first introduce the two major categories of software testing - white box technique and black box testing.
In the white box technique, the tester knows the design/internal structure/implementation of the software being tested. Developers design the test cases using programming skills and an internal viewpoint. White box testing has two specific criteria - data structure sensitization and the execution path. People also call these loop testing, path testing, data flow testing, etc.
So, if we consider the purpose and definition of unit testing, it belongs to the white box testing category. Besides, unit tests sensitize data structures and the execution path, which are criteria of white box testing.
Contrastingly, in the black box technique, the tester barely knows anything about the tested software. Without any knowledge of the code/program/internal structure, testers will check the behavior or functionality of your software based on the expected outcome. So, without a doubt, functional testing belongs to the black box technique.
Executing a unit test in a TDD (test-driven development environment is quite complicated. Your developers should write unit tests before the production code in a TDD. So based on your software requirements, developers have to think about the code design in advance.
Hence, if your code design is unclear initially, it will evolve eventually and force you to do the same test again. For instance, if you're dealing with algorithms that often change, it would be best if you postpone unit testing until you gather some idea about the code design.
In reality, there are other integrations and dependencies we have to consider, such as database, UI, and so on. In such scenarios, TDD becomes pretty difficult and includes various abstractions like MVP/MVC pattern, programming to an interface, mock objects, etc. all this requires a good deal of expertise and knowledge as developers need to write huge volumes of unit tests, more than the production code at times.
Excluding such dependencies, testing trivial code becomes very complicated with unit tests. The reason is code units are most likely to gather together and start interacting with other units.
While mocking out all the dependencies is viable in unit testing, the story is something different in functional testing types. Let me give you an example. If you try to test a screen that processes the data from the cellular network, it'll not work offline. Executing a functional test becomes very complex in such scenarios.
Developers write a test to run the new code, and in such a process, they substantially apprehend the work. For instance, if your developer breaks the code in six months, they can run the test to secure the code. That's how unit testing helps you prevent regression.
So, unit tests help you identify potential defects in your system through a bug report so that developers don't need to spend extra time and resources in the long run.
Functional testing focuses on a "happy path" - ensuring all the crucial user functionalities, such as signups, logins, purchasing workflows, are working as expected. It has different subsets, each with specific advantages.
Take integration testing, for example, that ensures compatible working of all the integration. Smoke testing is another type of functional testing that can help you check essential software features, reduce regression, and save time.
Test coverage holds great importance in software project delivery. It's a crucial metric that has different purposes of serving in both functional tests and unit tests.
With a test coverage tool, you can easily keep a check on what part of the code is exercised and what not during the testing process. That's why we can call it code coverage in the context of unit testing. So, if your developers get high code convergence, chances are they have built and maintained a good app. In certain cases, high test coverage also enhances the code quality, but that doesn't mean poorly written code with high test coverage will result in improved code quality.
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In functional testing, you can track the design quality of test cases with test coverage. By establishing traceability between test cases and the requirements, functional test coverage will inform you about what features are still in progress and what features are complete. While you might not get a chance to know the number of executed code lines, this kind of test coverage information can be easily accessible to you.
You can't replace unit tests with functional tests, but they formulate the solid base of the software QA process audit. It would be best if your developers write the test and the code at the same time. In this regard, I should let you know about TDD (Test Driven Development), a software development approach that prioritizes writing tests before codes.
Among many of its advantages, unit testing allows you to refactor your code and inform in case you break anything.
After you have successfully executed the unit tests, integration testing comes into the picture. So in this sense, you can run functional tests on the feature when two modules interconnect with each other. You may run a unit test to check a specific function or an integration test to test the compatibility of two functions.
Keep in mind that you can run as many unit tests as you want, but you can have only a small number of them when it comes to functional testing.
To be honest, I'm not going to present a universal formula to maintain a decent balance between these two software testing types. Based on the conditions and your project requirements, the number of tests can differ. Despite the common software testing myths, what ultimately matters is whether the tests are delivering the value you expected.
If you rely too much on functional testing, it might affect the software quality. Sure, the world of software development is advancing, but one thing that has not still gained much ground is software quality assurance. This is the reason a lot of established software development companies prefer functional testing over unit testing.
So, what if you decide to completely neglect unit tests and over-depend on functional tests? Let me show you how this decision will decrease the software quality:
I would suggest you fulfill three basic objectives whenever you take on a software development project - efficient workflow, flawless features, and clean and maintainable code. You can find the right balance between functional and unit testing by preparing a set of questions and presenting it to the project manager to meet the goals.
Here are a few considerations you can think about to fulfill these objectives:
Ultimately, the testing pyramid is the principle visual support to maintain a decent balance between all three kinds of software testing. As you can see, the bottom of the pyramid consists of unit tests, making the most of your tests. As you go up, the tests get bigger but simultaneously, the width of the pureed gets smaller, meaning the number of tests becomes smaller.
According to Google, a 70/20/10 split would be the best approach. This means you should go for 70%-unit tests, 20% integration tests, and 10% end-to-end tests. The combination can vary from team to team, but it should maintain the pyramid structure as a general rule.
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Today, every client expects software development companies and their developers to create software of prime quality. And such demands have propelled the companies to come up with different testing methods as part of the development process.
If you want to achieve clean and bug-free code faster, unit testing is the key. It will basically tell you where the problem lies in the code. Yes, your developers need to spend extra hours to fix the errors, but in the end, it will be worth all your time and efforts.
On the contrary, functional testing is complex and slow, but it guarantees that your software will function as per the requirements. If there's an issue with the functionality, it will inform you.
So, both of these software testing methods consist of their assets and liabilities. It's up to you how you're going to balance them and deliver the finest software to the end-users. And an experienced software testing company, Radixweb can help you here. Our skilled software testers can enhance the development experience and product quality for you so that you can constantly stay tuned with the latest market trends. Let's start discussing your testing and QA needs, shall we?
Indu Nair works as a professional Bug Hunter at Radixweb. She is an expert in manual testing, agile testing, test case, and bug report writing. With 7 years of experience and a strong command over tools like JMeter, Rest Assured, TestNG, Appium, and Selenium, she guarantees seamless and reliable test automation. Her outstanding skills ensure that software releases are bug-free, efficient, and secure. Indu's comprehensive approach makes her an invaluable member of Radixweb’s QA team.
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