how are jest test cases running code example

Example 1: jest run specific test

From the command line, use the --testNamePattern or -t flag:

jest -t 'fix-order-test'
This will only run tests that match the test name pattern you provide. It's in the Jest documentation.

Another way is to run tests in watch mode, jest --watch, and then press P to filter the tests by typing the test file name or T to run a single test name.

If you have an it inside of a describe block, you have to run

jest -t '<describeString> <itString>'

Example 2: testing with jest

npm i jest --save -dev
-> In Package.json change the Script object(watchAll - jest will run auto)
"test" : "jest --watchAll"
-> test file should be named such way that re used by jest can recognize it
like filename.<test> or <spec> or skip it.js
Ex: sum.test.js or sum.spec.js or sum.js
-> require the target for testing file in this test file then enjoy testing.
-> visit jestWebsite-> Docs.