Introduction

Unit testing is testing the components in isolation. It helps in testing the edge cases of the component and functionality of the application. Unit testing allows you to test all the flows – success and error flow in the component. This makes sure that the component handles the error gracefully and as expected.

Unit test usually consists of following components

  • Test runner
  • Test utility
  • Assertion library
  • Mocks library
  • Coverage Reporter

Test runner is used to run the tests. It allows you to configure the setup, executes the unit tests, and provides the output. Example – Jasmine, Mochajs, Jest, Karma

Test utility provides helper functions which makes it easier to test the component. Example – Enzyme, React Testing library

Assertion library allows you to assert the conditions. Example – Expect, Chai

Mocks library allows you to mock the component functionality. Jest, Sinon

Coverage reporter provides the coverage of the unit test cases in nice format containing details like coverage by line, flow, file etc. It also provides output in console, csv format, excel and other such format. Example – Jest, Istanbul

Why Jest is important in unit testing in React

In React, Jest provides the functionality of test runner, assertion library, mock library and coverage reporter. Jest is based upon Jasmine library. 

Jest does the job of executing the test cases, assertion, mocking and coverage. So understanding Jest is important step in writing unit test cases in React.

Introduction

Unit testing is testing the components in isolation. It helps in testing the edge cases of the component and functionality of the application. Unit testing allows you to test all the flows – success and error flow in the component. This makes sure that the component handles the error gracefully and as expected.

Unit test usually consists of following components

  • Test runner
  • Test utility
  • Assertion library
  • Mocks library
  • Coverage Reporter

Test runner is used to run the tests. It allows you to configure the setup, executes the unit tests, and provides the output. Example – Jasmine, Mochajs, Jest, Karma

Test utility provides helper functions which makes it easier to test the component. Example – Enzyme, React Testing library

Assertion library allows you to assert the conditions. Example – Expect, Chai

Mocks library allows you to mock the component functionality. Jest, Sinon

Coverage reporter provides the coverage of the unit test cases in nice format containing details like coverage by line, flow, file etc. It also provides output in console, csv format, excel and other such format. Example – Jest, Istanbul

Why Jest is important in unit testing in React

In React, Jest provides the functionality of test runner, assertion library, mock library and coverage reporter. Jest is based upon Jasmine library. 

Jest does the job of executing the test cases, assertion, mocking and coverage. So understanding Jest is important step in writing unit test cases in React.