spying on node child_process using jasmine

Question

I am new to nodejs and jasmine. Working on a small project for learning javascript/node and jasmine. I am trying to spy on the object child_process in node and see the method 'spawn' is called with the arguments specified.

The jasmine error reports that the spawn is never called when the object (Nndb in this case) that invokes the spawn method is called. But the actual work is performed by the child process as I see the results printed in the console.

Here is the failure I see when running the jasmine-node script:

Failures:

1) scrape for xyz spawns child process Message: Expected spy spawn to have been called with [ '../src/scrape_nndb.js', 0 ] but it was >never called. Stacktrace: Error: Expected spy spawn to have been called with [ '../src/scrape_nndb.js', 0 ] but >it was never called. at null. (/Users/arun.bakt/skunkWorks/scraping/spec/nndb_spec.js:30:41) at Timer.listOnTimeout [as ontimeout] (timers.js:110:15)

Finished in 6.024 seconds 1 test, 1 assertion, 1 failure, 0 skipped"

The jasmine test file for it:

require('../src/nndb.js');

describe("scrape for XYZ", function() {

    var child = require('child_process');

    it("spawns child process", function() {

        var nndb = new Nndb();
        var child_process =  nndb.child_process;
        spyOn(child_process, "spawn");

        runs(function(){
            flag= false;
            nndb.scrapeForXYZ('../src/scrape_nndb.js', 0);
            setTimeout(function() {
                flag = true;
            },6000)
        });

        waitsFor(function(){
            return flag;
        }, "Scraping done", 6000);

        runs(function(){
            expect(child_process.spawn).toHaveBeenCalledWith('../src/scrape_nndb.js',0);
        });
    });

});

The file nndb.js that is being tested below:

var StringDecoder = require('string_decoder').StringDecoder;

var decoder = new StringDecoder('utf8');

var child_process = require('child_process');

Nndb = function() {

    this.child_process = child_process;

    this.spawn = this.child_process.spawn;

};

Nndb.prototype.scrapeForXYZ = function( phantomScriptToRun, offSet) {


    var child =  this.spawn('phantomjs', [phantomScriptToRun, offSet]);

    child.stdout.on('data',function(data){

         console.log("MATCH "+decoder.write(data));

    });

    child.stderr.on('data', function (data) {
        console.log('stderr: ' + data);
    });

    child.on('exit', function (code) {
        console.log('child process exited with code ' + code);
    });

    return 0;

};



exports.Nndb = Nndb;

Well, the spy didn't get set up properly - I'm not sure why not. If the spy was working, the function's actual code would *not* have run. Spies, by default, replace the functions they watch, rather than watching and reporting. If you want the function to run normally as well, you need to do something like `spyOn(child_process, 'spawn').andCallThrough();` — user1618143, Dec 11 '13 at 15:45

score 0 · Accepted Answer · answered Dec 11 '13 at 15:55

0

Oh, I see the problem. You create nndb, and nndb sets nndb.spawn equal to nndb.child_process.spawn. Then you set a spy on nndb.child_process.spawn, but because nndb.spawn has already been copied off of it, the spy isn't applied to both. When nndb.scrapeForXYZ calls nndb.spawn, the spy is unaffected.

Try this:

it("spawns child process", function() {

    var nndb = new Nndb();
    var child_process =  nndb.child_process;
    spyOn(nndb, "spawn");

    //...
        expect(nndb.spawn).toHaveBeenCalledWith( //...

}

answered Dec 11 '13 at 15:55

user1618143

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Hi, What you have observed is correct. Slight modification in it is that I still have to spy on child_process and not nndb. Nndb is the test subject. After removing the line "this.spawn = this.child_process.spawn;" from the nndb constructor and adding "spyOn(child_process, "spawn").andCallThrough();" made the test pass. Thank you for your answer. Now I have to figure out how to test the child.stdout.on and child.stderr.on methods in the spawned child_process – arunbakt 9 hours ago – arunbakt Dec 12 '13 at 06:45

spying on node child_process using jasmine

1 Answers1