Unit Test vs Integration Test​

Difference between Unit Test and Integration Test​

Unit testing is a test process by which each unit of source code is tested to determine if it is ready for use, while Integration testing monitors the Integration between software modules. This helps to reduce the costs of bug fixes as bugs are found during the early stages of the life cycle. It is a software test methodology that integrates and measures individual units of a system as a group. For integration testing test stubs and test drivers are used for the integration testing. Usually Top down method and Bottom up method are been used to perform the integration testing.

Unit Testing

It​ is basically testing a small piece of code or a function/method to check whether it is working fine or not. Unit testing is also known as Component or Module testing. It does not involve any interaction with the dependencies like network, other software components, database, etc. These unit tests are narrow, simple and generally written by the developer or the person writing the same piece of code. These are written to check the code or the function written is working as expected or not. Unit testing is the first level of testing and it helps a lot in reducing the time of both the testers and developers in filing and fixing a bug in the later stages of testing.

Unit testing starts with the checking of the basic functionality of what the code is intended to do and then followed by nonfunctional and coverage issues. No bug is logged for the issues found in the Unit testing. It is the backbone of testing and a good unit test not only prevents bugs but also helps in good code design.

Integration Testing ​

It is basically testing how the different parts of an application work together. It checks the interfaces and interactions between different modules of an application. As the name suggests integration testing integrates the parts of an application and then test them as a whole. In real scenarios, integration testing comes after the unit testing. When the different modules of an application are unit tested and are working fine, then they are gone through integration testing to check whether together they are working as expected and interacting with each other properly using the real dependencies like network, database, hardware, etc.

Integration testing is quite complex and harder as it requires a lot of setups. That’s why integration tests are difficult to write and test than unit tests. This testing is very important as the whole integrated system/software is delivered to the client and not the small units(pieces of code). It uncovers a lot of bugs because many times individual components work fine but face issues while interacting with each other like data exchange, function calling, hardware issue.

Head to Head Comparison between Unit Test and Integration Test​ (Infographics)

Below is the Top 9 Comparison between Unit Test vs Integration Test​ :

Key Difference between Unit Test and Integration Test​

Below are the lists of points, describe the key differences between Unit Test vs Integration Test​

1. Unit testing uncovers the issues in the individual functionality or a specific module whereas Integration testing uncovers the bugs arise due to the interaction of two modules or an application as a whole.
2. Issues found in Unit testing can be instantly fixed by the developer as the issue is in a specific module or a particular code but issues found in Integration testing takes a lot of time and cost to fix as it becomes difficult to find where exactly bug has arisen as different modules are developed by different developers.
3. It is very cost-effective to find and fix the issues found in Unit testing whereas in Integration testing bug fixing is quite costly.
4. Unit testing starts from module specifications whereas Integration testing starts from Interface specifications.
5. An approach for Unit testing is test-driven development in which test cases are created first and then the development is done according to that whereas approaches for Integration testing are the Big Bang approach, top-down approach, bottom-up approach, and hybrid approach.
6. For Unit testing, accessibility of code is required as it tests the code written whereas in Integration testing no code access is required as it tests the interactions and interfaces between the modules.
7. Test basis for unit testing is a component requirement, code, and detailed design whereas the test basis for Integration testing is software and system designed detailed system architecture and workflows/use cases.

Unit Test vs Integration test Comparison Table

Below is the topmost comparison between Unit Test vs Integration test

Basis of Comparison	Unit Test	Integration test
Functionality	In Unit test, small module or a piece of code of an application is tested	In the Integration test, individual modules combined together and as a group, they are tested
Speed	Unit tests are faster to write and execute	Integration tests are comparatively slower to execute
Complexity	Unit tests are less complex to write and execute	Integration tests are more complex to write and execute
Involvement of dependencies	Unit tests do not require any involvement of outside dependencies like database, network, etc	Integration tests require the use of real dependencies in order to perform testing like test database, hardware, etc
Test Conductor	Unit tests are generally conducted by the developer or the person written that particular code	Integration tests are conducted by the separate team of testers
Order of Testing	Unit testing is performed in the starting phase just after an individual module or a piece of code is developed	Integration testing is performed after the unit testing of individual modules are completed and before the start of System testing
Maintenance	Unit tests have very low maintenance	Integration tests have very high maintenance
Scope	The unit test has a very narrow scope as it covers only a piece of code/part of an application	Integration tests have a wider scope as it covers the whole application
Knowledge of the code	The person doing the Unit testing has full knowledge of code and internal functionality and hence known as white box testing	A person working on Integration testing does not have knowledge of code but has knowledge if expected output and overall functionality and hence known as black-box testing

Conclusion

I think that the above points made it clear about both Unit test vs Integration testing. We cannot say that anyone testing is more important and useful than others. Both testings serve their purpose and are correlated. Before delivering any software to the client, it is important that each module of the software works fine and software as a whole should work as expected. For example, In the case of an e-commerce website, login, add to cart, payment modules individually should work fine and all the modules of an e-commerce website needs to properly interact with the database and payment module. So for the least risk of failure, both testing should be performed rigorously, on time and should not be delayed.

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