What is Unit Testing?

It is a type of software testing in which a small piece of code is tested to see if the code works as expected. Unit Testing is done during the development of an application and is typically performed by the developer.

It helps to reduce the cost of bug fixes, as bugs are identified early in the development lifecycle.

Unit test
Figure 1 – Unit Test

What is Integration Testing?

As its name implies, an Integration Test verifies that the interface between two software units or modules works correctly. It covers the whole application.

Integration Testing comes after the Unit Testing and before System Testing.

Integration test
Figure 2 – Integration Test

Unit Testing VS Integration Testing

Unit test vs integration test
Figure 3 – Unit Test VS Integration Test

To clarify the distinction between the two, let's look at the comparison table:

Unit Testing Integration Testing
It tests small modules or a piece of code of an application Individual units of a program are combined and tested as a group
It's a quick write-and-run test It is slower to run
Typically performed by the developer It is carried out by a separate team of testers
It can be performed at any time It is usually carried out after Unit Testing
It has very low maintenance It has very high maintenance
It is very limited in scope, as it only covers a piece of code It has wider scope as it covers whole application
It pays attention to the behavior of single modules It pays attention to integration among modules
Finding errors is easy Finding errors is difficult
Tester knows the internal design of the software Testers don't know the internal design of the software
It is white box testing It is a black box testing

Key Differences

  • Integration Tests will help to verify the overall system while Unit Testing is a testing method by which individual units of code are tested.
  • Issues found in Unit Testing can be instantly fixed but issues found in Integration Testing take a lot of time and cost to fix as it becomes difficult to find where exactly a bug has arisen.
  • Unit Testing is a kind of white box testing, whereas Integration Testing is a kind of black-box testing.
  • For Unit Testing, accessibility of code is required, as it tests the written code, while for Integration Testing, access to code is not required, since it tests the interactions and interfaces between modules.

Key Similarities

  • Neither of these two tests can be considered more important than the other. Both the Unit Test and Integration Test are very important and useful.
  • They should be performed rigorously, on time and should always be an integral part of the development process. It is always important to remember that both tests are correlated.
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