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Differences between API Testing and Unit Testing

Last Updated : 23 Jul, 2025
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API Testing

An application programming interface (API) is a type of programming interface. API can be thought of as a bridge between two software systems that allows them to communicate. API testing entails evaluating application programming interfaces (APIs) both independently and as part of integration testing to see if they fulfill functionality, reliability, performance, and security requirements.

  • API tests are only run when the build is complete.
  • As the user interface with which an end-user will interact, API testing must represent the system as a whole.
  • API testing is a type of black-box testing that focuses solely on the system under the test's ultimate output.

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Methods of API Testing

  • Security testing
  • Automated testing
  • Discovery testing
  • Usability testing

Tools used in API Testing

  • REST assured
  • Tricentis Tosca
  • Ping API
  • Postman
  • Katalon Studio
  • Soap UI

Unit Testing

Its goal is to test each individual module as it becomes available and to verify whether the module carries out the mandatory functionality. Unit testing can be carried either manually or automatically. 

  • Ensure that the code is correct.
  • Aid developers in comprehending the code base and allowing them to make changes fast.
  • Save money by fixing bugs early in the development cycle.
  • Unit testing has two types:
    • Manual testing
    • Automated testing

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Tools used in Unit Testing

  • NUnit
  • EMMA
  • PHPUnit
  • Jtest
  • Junit

Difference between API Testing and Unit Testing

API Testing

Unit Testing

Access main functionality of the system employed by end-user and its more comprehensive as it is tested from user's perspective.Used to test each unit performs as expected or not. It is less comprehensive as it is tested in isolation.
It is carried out by the QA team and testing is complex involving multiple systems and applications.It is carried out by developers and comparatively less complex as the code is tested early before integration and system testing.
The functionality has been tested from beginning to end including entire product and features making it more time consuming.Functionalities are put to the test individually and is maintainable.
Most of the time it is Black Box Testing.This is White Box Testing.
Entire API functions are put to the test.UI testing is also a part of the process which helps in testing all the edge cases.
All functional issues are thoroughly examined.Only the most basic functions are put to the test
Broader in scopeThe scope is limited.
After the build is finished, it is run.Usually performed prior to check-in. 

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