Both unit testing and integration testing are essential for any software development because each uses a different method to test a software application. 

However, neither one nor even both, can ever completely replace functional testing. 

Unit Testing Vs Integration Testing Vs Functional Testing 

Unit testing is the process of testing individual modules of an application in isolation (without connection with dependencies) to ensure that the code is working properly. 

Integration testing includes specifying whether or not various modules function properly when combined as a group. 

Functional testing entails testing a subset of the system’s functionality (which may interact with dependencies) to ensure that the code is performing as expected. 

Functional tests are similar to integration tests; however, they refer to tests that check the complete application’s functionality with all of the code running at the same time, thereby acting as a super integration test. 

Unit testing examines a single system component, whereas functionality testing examines the behavior of an application in relation to the desired functionality defined in the system requirement specification. Integration testing, on the other hand, considers checking integrated modules in the system. 

Most importantly, to maximize return on investment (ROI), your programming language should have as many unit tests as possible, fewer integration tests, and as few functional tests as possible. 


Unit tests are simpler to write and execute. As illustrated in the above pyramid, the time and effort required to implement and manage the tests grow from unit testing to functional testing. 

Now, let us now take a technical example for each testing approach of a login page: 


Almost all web applications demand users/customers sign in. Every application has a “Login” section that contains the following elements: 

  1. Account/Username 
  2. Password 
  3. Login/Sign-in Button 

For Unit Testing, the following may be the test cases: 

  • The length of the username and password fields.
  • The input field values must be correct.
  • Only after valid values (Format and lengthwise) are entered in both fields enables the login button.

The following may be the test cases for Integration Testing: 

  • The user should be directed to the welcome page or home page after entering proper values and pressing the Login button.
  • Successful completion of unit and integration testing, the following additional test approaches can be considered for functional testing: 
  • The testing is checked, i.e., can the user login by clicking the login button after inputting a valid username and password?
  • Will there be a welcome message displayed following a successful login?
  • Is there an error message that should appear if a login is invalid?
  • Are there any site cookies saved for login fields?
  • Can an inactive user log in?

There are numerous other situations that a functional tester might consider while performing functional testing. A developer, on the other hand, cannot take on all scenarios while writing Unit and Integration test cases. 

As a result, even after unit and integration testing, there are several scenarios that have yet to be evaluated. 

It is now time to look at the main differences between the three, Unit, Integration, and Functional testing. 

The distinctions between unit testing, integration testing, and functionality testing can be classified as follows: 

Purpose: Unit testing examines the application’s most fundamental unit, each module, individually. Integration testing analyzes how two or more modules work together to complete tasks. Functional automation testing examines the behavior of the application as a whole. 

Complexity: Unit testing has a simple language and is simple to write so it comprises the tiniest of codes. While integration testing is slightly more difficult than unit testing, functionality testing is the most difficult of the bunch. 

Testing techniques: White box testing methods are used in unit testing. Only black-box testing approaches are used in functional regression testing. Integration testing employs both black and white-box testing approaches, often known as grey-box testing. 

Errors covered: Unit tests can address issues that arise often in several modules. It eliminates the possibility of any problem going undiscovered. The faults covered in integration testing include bugs that occur when integrating multiple modules. It is unusual for an issue to escape. Issues that restrict an application’s performance are detected during automated functional testing. Problems based on scenarios are also tested here. Because the list of tests to be executed is unlimited, there is the greatest possibility of issue escape here. 


These three methods of testing are all related. 

To get comprehensive coverage, unit tests for paths/lines of code are necessary, as well as functional and integration tests to ensure that the ‘units’ work together cohesively. 

Mammoth-AI brings to you comprehensive app testing services to deliver a flawless digital experience to users. 

Hope this post has provided you with a clear understanding of unit, integration, and functional testing, as well as their distinctions, however, there is much more to these types of testing!! 

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