Unit Test vs Integration Test: What are the differences?

Worldwide, thousands of applications are developed and tested every day. To ensure the highest levels of reliability, the products undergo a wide range of tests. Globally, businesses increasingly rely on development and testing, so understanding this aspect of testing becomes crucial. 

A key difference between unit testing and integration testing is the number of components involved. Now let’s look deeper into these concepts.

What is Unit Test? 

Unit testing is a process of testing an individual code of an application in isolation to ensure that the code is working fine. The testing is done in isolation to avoid any code interaction with dependencies.

• The primary characteristic of a unit test is that it is performed in isolation; that is, the code under test should not rely on external systems. 
• Unit tests are designed to ensure the code meets the developer’s expectations as intended.
• In addition, unit tests are carried out early in the development process to identify and eliminate the cost of bug fixes when the individual components are merged and tested as an entire system. 
• Unit testing is easily executed in comparison to Integration tests. 

Let’s take an analogy to understand Unit Testing further. You have a Car, and the tires are checked before integrating it into the Car. This is analog to a unit test in software. Let’s understand it deeper with a real example we may face while testing a website. For instance, the login component of a website usually has elements like a username, password, and a login button.

We have understood that unit tests are done for individual components in isolation; in this case, the unit tests will cover portions such as ensuring that the field length is appropriate, input values are valid, the button is working fine, and more. 

What is an Integration Test?

In integration testing, we ensure that a group of modules works fine when integrated. Unlike in unit testing, an individual module is tested in isolation.

• Integration testing covers the connection between two or more modules. 
• It is suitably carried out in large-scale industries with individual software vendors or ISVs.
• The sole purpose of Integration testing is to ensure all the modules work fine without disturbing the functionalities of the modules that are put together. 

Let’s take the previous analogy, in the car, if your tires are inserted, and then it is checked if these models of tires are working well along with this model of car, then it is integration testing. 

Also, let’s take the previous example of the login component. To ensure that the login button is only clickable when some entries are filled in the username and password parameter, it is considered Integration testing as it relies upon integrating other components in the test.  

In companies, it usually happens that several developers are working on different components, so it becomes essential to perform integration testing when all the components are brought under one roof and work co-dependently. 

Integration testing is of two types. Let’s take a brief look at both of them. 

Big-bang Approach

In this type of Integration testing, all the components are coupled and tested. The main difference between this and system testing is that it is carried out only after unit testing to ensure all the module connections work fine. In System testing, the entire system is tested simultaneously, considering all the parameters. 

Incremental Approach

In this type of Integration testing, unlike the Big-bang approach where all the modules are coupled and tested at once, in this approach, the modules are integrated one by one, and errors are identified using stubs or drivers. It is further divided into three more parts. 

1. Top-down approach: This testing of modules is done from top to bottom, where the unavailable modules are replaced with the stubs. 

2. Bottom-up approach: In this, modules are tested from bottom to up, where the unavailable modules are replaced with the drivers. 

3. Hybrid approach: It is also known as sandwich testing. The main layer comprises of software’s features. It takes advantage of both top-down and bottom-up approaches.  

Key Differences between Unit Test and Integration Test 

On continuing our discussion over unit testing vs integration testing, let’s also understand some key differences between the both.

Advantages and Disadvantages of Unit Test and Integration Test

Based on the abovementioned differences, it is generally easier to perform Integration testing and catch all errors than to waste time performing unit testing. It takes a very long time for Integration testing to fix tiny errors that can be captured by Unit testing. 

Now that we’ve established the key differences between unit tests and integration tests, let’s examine their advantages and disadvantages.

Advantages and Disadvantages of Unit Testing

Advantages and Disadvantages of Integration Testing 

Key Takeaways

In this example, we understood the difference between unit test and integration test. Both of the testing processes are equally important for the product. The higher efficiency from these tests is achieved when they are combined effectively. 

• The process of writing and executing unit tests is generally faster, whereas analyzing the connections between several modules in the software is complex in integration testing.
• One benefit of unit tests is their speed, deterministic nature, and precise results.
•  In contrast, an advantage of integration tests is that they cover the border scope that unit tests cannot cover.

Remember that Incorporating any testing practices is faster and easier to execute on a real device cloud. As far as possible, tests must be run in real user conditions to ensure complete accuracy of results.

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