how should i do asynchronous unit testing?

Question

I am using pg-promise. i am learnner please excuse if it seems trivial to you. how can i wrtie unit test for. it errors out data is undefined. i have been making connection in js file and export that module.another js file use to query against database and fetch result set. code is working as expected having issue how can i write unit test with mocha and chai.

test1.js
var dbConn= pgp(connUrl);
module.exports = {
    getconnect: function () {
        return dbConn;
    }
};

test2.js

module.exports = {
    getData: function (req, res) {
      db.getconnect().query(sqlStr, true)
                .then(function (data) {  
                    console.log("DATA:", data);
                    return data; 
                  } } }

unittest.js

describe("Test Cases", function (done) {

    it('retrieve response', function (done) {
        var req = {};
        var res = {};
        test2.getData(req, res);    
        // how would i retrieve value of data from test2.js so i can test
        done();
    });
});

how would i retrieve "data" value from test2.js inthe unittest.js

@vitaly-t. would you please suggest how should i write unit test? — aka, May 21 '16 at 21:39
The right question you should ask - how to write tests for an asynchronous library. That's not really relevant to pg-promise. In the meantime, you can look at [pg-promise tests](https://github.com/vitaly-t/pg-promise/tree/master/test) for an example, they way the library tests itself. — vitaly-t, May 21 '16 at 21:45
It's weird that you have an async function that only logs an output but does nothing else. If the output to stdout is what's important then test that, don't test the function since the function returns nothing which makes it untestable. I'd personally write that specific test as a bash script since that's the simplest way to do it. If you HAVE to write it in js then write it the way you'd write a bash script: exec the script and grep it's stdout. — slebetman, May 22 '16 at 16:00
@slebetman i want to test value "data". i dont know how to return value of "data" to unitest.js — aka, May 22 '16 at 18:41
A good practical example: [Cleaning the database in-between Mocha tests with pg-promise](https://coderwall.com/p/axugwa/cleaning-the-database-in-between-mocha-tests-with-pg-promise). — vitaly-t, Apr 06 '17 at 20:40

vp_arth · Accepted Answer · 2016-05-22T19:40:34.457

Your getData must return the promise. Client code will be able to recognize the moment it's finished(resolved).

module.exports = {
    getData: function (req, res) {
      return db.getconnect().query(sqlStr, true)
                .then(function (data) {  
                    console.log("DATA:", data);
                    return data; 
                  } } }

test:

describe("Test Cases", function () {
    it('retrieve response', function (done) {
        var req = {};
        var res = {};
        test2.getData(req, res).then(function(data){
          // test of data returned
          done(); // finish test
        }).catch(done);// report about error happened
    });
});

If you don't need to any process of data in your module, you can to remove whole .then section without any functionality changes.
But if you want to preprocess data - don't forget to return it from each chained .then.

If your test library requires stubs for async stuff, you can use async/await feature to deal with it.

it('retrieve response', async function(){
  try {
    var data = await test2.getData(req, res);
    // test data here
  } catch (e) {
    // trigger test failed here
  }
});

Or stub it, something like this:

var dbStub = sinon.stub(db, 'getConnect');
dbStub.yields(null, {query: function(){/*...*/}});

if your `node.js` version supports `async/await` you can use it. Added to answer. — vp_arth, May 22 '16 at 19:31

score -1 · Answer 2 · answered May 22 '16 at 18:57

-1

If you have a function returning promise then you can use await in your tests:

describe("Test Cases", function (done) {
    it('retrieve response', async function (done) {
        try {
          var data = await test2.getData();
          // check data constraints ...
          ...
        } catch(err) {
          ... 
        }
        done(); // finish test
    });
});

answered May 22 '16 at 18:57

c-smile

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it errors out something like missing ). i checked every where i am not missing any parenthesis – aka May 22 '16 at 22:38

how should i do asynchronous unit testing?

2 Answers2