async.test.js

/**
 * ************************  CHAPTER 8 ************************************************
 * Async Code
 * ************************************************************************************
 * 
 * 
 * @see https://jestjs.io/docs/en/api#testname-fn-timeout
 * @author Abhijeet Bhagat
 * 
 * NOTE :- if you need to run tests only in this test suite then use following command
 * ****************************** COMMAND ********************************************
 * ___________________________________________________________________________________|                                                                                   
 *               npm test -t async.test.js                                         |
 * ___________________________________________________________________________________|
 */ 

 //In this chapter in order to give async behavior i am going to use setTimeOut
// The following function uses setTimeout to return an object/array after 2 seconds.
function getArrayAsync(callback){ 
setTimeout(()=>callback([1,2,3,4,5]),2000,callback);
}

/**
 * if we use test like this it will fail as we will get undefined
 *
  test('test async', () => {
  function runtest(data) {
    expect(data).toContain(3);
  }

  getArrayAsync(runtest);
});

 */

 //SO... in order to test async code
 //instead of putting the test in a function with an empty argument, use a single argument called done

 //NOTE ***** USE OF DONE

test('test async', done => {
    function runtest(data){
        // const data = getArrayAsync();
        expect(data).toContain(3);
        console.log(data);
        done();

    }
    getArrayAsync(runtest);
});


//NOW let's see promisified async code
function getArrayAsyncUsingPromise(){ 
    return new Promise((resolve,reject)=>{

        setTimeout(()=>resolve([1,2,3,4,5]),2000);
    });
    }

//If your code uses promises, 
//there is a more straightforward way to handle asynchronous tests. 
//Return a promise from your test, and Jest will wait for that promise to resolve. 
//If the promise is rejected, the test will automatically fail. 

test('async using promise',()=>{
    return getArrayAsyncUsingPromise().then((data)=>{
        console.log(data);
        expect(data).toContain(3);
    })
});

/**
 * Be sure to return the promise - if you omit this return statement, 
 * your test will complete before the promise returned from getArrayAsyncUsingPromise resolves and then() has a chance to execute the callback.
 * If you expect a promise to be rejected, use the .catch method. 
 * Make sure to add expect.assertions to verify that a certain number of assertions are called.
 * Otherwise, a fulfilled promise would not fail the test.
 */


 /**
  * You can also use the .resolves or .rejects matcher in your expect statement,
  *  and Jest will wait for that promise to resolve. If the promise is rejected, the test will automatically fail.
  */

  //The same example above using .resolves matcher
  //NOTE it is RESOLVES and not RESOLVE
  test('async using promise using resolves matcher',()=>{
    return expect(getArrayAsyncUsingPromise()).resolves.toContain(3);
    });



/**
 * Alternatively you can also use the async/await syntax.
 * in case of async/await you don't have to return the promise 
 */

test('async using promise using async/await',async ()=>{
    const data =  await getArrayAsyncUsingPromise();
     expect(data).toContain(3);
    });

// async and await can be combined with .resolves matcher

test('async using promise using async/await with .resolves matcher', async () => {
    await expect(getArrayAsyncUsingPromise()).resolves.toContain(3);
  });

/**
******************************** Quiz ***************************************************
* 1. how is 'done' used when dealing with the async functions that take a callback?
*  
*/

/**
* next go to
* @see https://github.com/bhagatabhijeet/jestSamples/blob/master/mocks.test.js 
* @see mocks.test.js
*/