2019-05-01+Web+Designer+UK

Test your JS with the Jestframework

ofrequiredattributes.Jest’slogictakesthe

snapshot’scontentsandperformsananalysis

againsttheobjectreturned— errorswillberaisedif

a mismatchis detected.Forthefollowingsteps,

startoutbyplacingthecodeshownnexttothis

stepinsideoftam.test.js.

it(‘is a small test’,() => {

test(‘Checksif we can divide’, () => {

expect(tam.divide(1,3)).

toBeCloseTo(0.333333333);

});

12. Run just one
    Should you ever feel like running one test, feel free
    to use the test.only function. It informs the runner
    that all other test cases are to be ignored — helpful
    and time-saving as your unit test suites grow.

test.only(‘this will be the only test that

runs’,

() => {

expect(true).toBe(false);

});

13. 
    

    Understanding snapshots
    As JavaScript object orientation entered mainstream
    developer conscience, more and more code
    adopted OOP principles.
    Sadly, verifying the correctness of objects gets
    tedious quickly — checking each and every
    member’s value by hand leads to long and
    difficult-to-handle test code.

    
    


14. 
    

    Content analysis
    Think of snapshots as a template containing a set

    
    

Jesttestscanalso

berunoutsideofa

package manager.

In this case, the Jest

command line utility

must be used — it

can only be run when

installed globally using

either NPMs or YARN’s

global install feature.

Once installed, visit

Jestjs.io/docs/en/cli.

Jest’s developer

team provide command

line users with dozens

of options intended to

tailor execution scope

to the needs of the task

at hand.

Entering ‘Jest

--findRelatedTests

path/to/fileA.js path/

to/fileB.js’ runs only

those tests which touch

the content of the files

passed in as arguments.

In addition to that, the

command line tool

can even analyse

local repositories and

run only these tests

affected by currently

uncommitted code.

Harness the

power of the

command line

Tutorials

const user= {

createdAt: new Date(),

id: Math.floor(Math.random() * 20),

name: ‘Tam HANNA’,

};

expect(user).toMatchSnapshot();

});

14

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