“The practice of writing code to test our code, and then run those tests in an automated fashion.”
Tests a unit of an application without its external dependencies.
External dependencies such as database, web services, message queue and so on…
Tests the application with its external dependencies.
Drives an application through it’s UI.
A popular tool for end-to-end testing is Selenium
Here you can see the importance of the unit test.
How to work with Jest framework?
Step 1: First, install the jest n pm package
Note: install jest on development environment only we are not going to install on production because this is for testing purpose only
Step 2 : Open package.json file and checkout scripts property
Scripts property define commands that we can execute in the command line
set jest to test the property of scripts
Jest is a command line interface that we used to run our tests.
When you run test jest command is executes and run all the files that match with “testMatch:/tests//*.js?(x),**/?(*.)(spec|test).js?(x)”.
Step 3: Create a route directory in the root
Create lib.js file into route directory and write a simple numeric function
Step 4: Create a test directory in the root
Create lib.test.js file into the test directory and write multiple test cases for absolute function
Here the test is a function provided by a jest which calls the absolute function with different input and matches expected output. if it’s matched it will return pass else return failed with discription.
here are few functions which are provided by jest to match the expected output
Step 5: Go to terminal and run test command
Here you can see all tests are passed.
In case of the test failed you will get output like this
Jest provides a different function to match expected output for string, array, objects and other data types you can checkout jest document for that.
Also, you can group test cases by using describe function just like below and you will get the same output. it’s good practice to use describe function because when you write multiple tests code gets ugly.
One last little secret add — watchAll to test command for automatically run all test after refactoring it will save you from the pain of hitting the same command again and again.
If you having difficulty in writing tests or have any doubt in your mind hit us always pleased to help you out.