Component Testing vs Unit Testing: Top Differences, Types, and Examples

Component Testing vs Unit Testing: Top Differences, Types, and Examples

Testing is a crucial part of every Software Development Lifecycle (SDLC). It takes center stage in CI/CD pipeline, allowing developers to release reliable, resilient, and safe software. Multiple testing types exist, such as End-to-End testing, Unit testing, Integration testing, Dynamic testing, and more. And among all these different types, two important ones, Component and Unit testing, emerge in the initial phase of SDLC. As they are closely related, developers need to understand their differences. This article will specifically focus on Component testing vs Unit testing to help you understand everything about these two tests.

We will discuss when to perform Component testing and when to go for Unit testing. You will also find examples, tools, and steps to implement these tests.

So, let’s begin by understanding Component testing.

What is Component Testing?

As the name suggests, Component testing involves analyzing multiple functions and code modules before they form software. It is a black box testing technique that evaluates the application without considering the code information.

Every software is a combination of different code components. A code component can either be made of two or more code units or a function, method, or class inside the application code bases. A simple real-life example of a software component is the login and signup component.

Before releasing software, it’s crucial to ensure all the components are working as intended. Component testing analyzes all these components (codes or functions) individually.

Who Performs Component Testing?

Usually, developers perform Component testing in the initial stage of SDLC just after the Unit testing. But even QA conducts the tests as well.

In Component testing, developers notice the component’s behavior in various use cases by providing multiple inputs. Similarly, the QA team performs it without the knowledge of the component’s underlying code logic and implementation. They observe a software component’s behavior by interacting with the application as end users.

When to Perform the Component Testing?

Component testing is done by developers when the software is ready for release to the testing team. There are a few instances where you should perform Component testing:

  • To test the components individually before the product’s release.
  • Alongside Regression testing to evaluate the functions of newly added components.
  • Before Integration testing check if each component is working properly

Component Testing Techniques

There are two types of Component testing techniques. They are based on the approach developers take to execute Component testing:

1. Component testing in Small: Component testing is performed by keeping other components in isolation, it is known as component testing in small (CTIS).

2. Component testing in Large: When an individual Component testing is carried out, and other software components are not isolated, it is known as Component testing in large (CTIL).

Component Testing Example

Let’s take an example, as shown in the picture below. It shows the sign-in page of a travel ticket booking website. Let’s call this page C1.

Component Testing Example - Login page
Login page of sample travel ticket booking website

If you navigate to the website signup page, it’s another component of the same application. Let’s call it C2.

Component Testing Example - Signup page

C1 and C2 are made of various code units working together to make the login and signup components functional, making up the application under test (AUT). Before moving ahead with testing C1 and C2 together (after integration), developers will separately analyze these two components. Individually, C1 and C2 must function as per the requirement with a set of inputs.

Now, let’s move on to the Unit testing definition to understand Component testing vs Unit testing better.

What is Unit Testing?

The software comprises smaller code units responsible for handling individual tasks and computations. A smaller code unit can be a function, method, or class. Software components and modules are made by integrating these code units, eventually building the functional software.

Developers perform Unit testing to ensure all the smaller code units function correctly. Unit testing is known as test-driven development (TDD) in software development. The test cases are written first; then, the bare minimum code is written to pass the test cases, followed by the final code. Unit testing is the first stage of testing for any software before it moves onto for further QA analysis.

A well-written Unit test behaves like good project documentation, making it easy to understand the individual code units. It also helps with migration, where a new project can reuse the code and test cases.

Who Performs Unit Testing?

Unit testing occurs during the SDLC’s initial phase by the team of developers. It is usually because Unit testing helps developers examine the code and provide feedback on whether the new features are working properly. It isolates the smaller code units to check and ensure it works correctly. Rarely does the QA team performs Unit testing.

When to Perform the Unit Testing?

As it stands, developers perform Unit testing during the application’s development stage. After one piece of code is complete that functions a certain way, they write Unit test cases to test that code. It helps to find the bug issue early in SDLC and saves the cost of performing the test later.

Unit Testing Techniques

Developers and the QA team follow various techniques that help them perform the Unit test effectively. While some Unit testing techniques focus on the code structure, others are attentive to the functionality.

Three Unit testing techniques cover every aspect of testing:

  1. Black Box Testing: This technique evaluates the AUT without knowing the background information or coding structure.

  2. White Box Testing: It checks for the functional behavior of the coding unit as per the sample input.

  3. Gray Box Testing: This type of testing involves White box and Black box testing, where the tester has partial knowledge of the code logic.

Unit Testing Example

Let’s take the same example as taken in Component testing. But this time, navigate to the homepage. Here’s the picture below.

Unit Testing Example
Homepage of sample travel ticket booking website

In the above image, you can see several individual units, such as the search flight button, the book now button, and multiple filters. All these have individual code units, which developers test separately before placing them on the homepage for the users.

Component Testing vs Unit Testing: Key Differences

While Component testing and Unit testing are done in the different stages of SDLC, they are closely related, but technically both are different. Here’s a table for you to easily understand Component testing vs Unit testing:

Component TestingUnit Testing
Involves testing each part or component of the application separatelyConsists of testing individual code units or modules
Developers and QA perform Component testingDevelopers perform Unit testing
Black box testingWhite box testing
Comes after Unit testing in SDLCFirst testing stage in SDLC
Validates test requirementsValidates design requirements
Does not serve as a reference document for future useServes as a good project documentation
Tester does is unaware of underlying code structureTester is aware of the underlying code
Difficult to detect issuesEasy to identify and catch defects


Although Unit testing and Component testing are closely related, they function differently and have differing purposes. The development team performs Unit testing in the initial phases of SDLC, ensuring the individual code units are working as per the requirement. On the other hand, Component testing comes right after Unit testing, which analyzes individual components for their functionality.

Both these test types focus mainly on evaluating the building blocks of an application very early in the development stage. Often, developers perform Unit and Component testing, but the task might fall on the QA team occasionally.

Lastly, there are several testing automation tools available that support Component as well as Unit testing. For instance, you can use Selenium to run test cases for your login and signup page for the example shown for Component testing. Similarly, to verify code units, you can rely either on your own Unit testing program or use tools like JUnit, NUnit, and Testsigma.

FAQ on Component Testing vs Unit Testing

Is component testing black box testing?

Yes, component testing is black box testing because the tester doesn’t know the components’ internal code logic and implementation. They perform by observing the behavior of software components in various use cases by providing different sets of input.

How is unit testing performed?

In unit testing, developers test smaller code units of the software to determine their working. A unit can be functions, methods, or classes in software. Unit testing is the first testing process in SDLC.

What is the purpose of component testing?

Component testing aims to ensure that every component, made of two or more units, works properly in isolation. It comes before Integration testing and after Unit testing.

Is component testing the same as functional testing?

No, component testing isn’t the same as functional testing. The software applications are extensive, and it is challenging to test the entire system. For the same reason, it may lead to many gaps in the test coverage. So, before we move into integration testing/functional testing, we must finish component testing.

Why is unit testing done?

Unit testing ensures that all the smaller software units work correctly. It catches the bugs early in the software development lifecycle and helps developers save time and money. A well-written Unit test also works as project documentation and helps to migrate the code base and test cases in newer projects.

What are the types of component testing?

Depending on the level of testing, component testing is of two types:

Component testing in large: Component testing in small (CTIS) is when a component is getting tested by keeping itself isolated from other components.

Component testing in large: Component testing in large (CTIL) is when a component is getting tested without isolating other software components.

Test automation made easy

Start your smart continuous testing journey today with Testsigma.