CODEWITHSUNDEEP
javascriptunit-testingmocha.jssinon
Dr.Legendaddy
Dr.Legendaddy

Reputation: 265

Fake calling of a function with specific arguments in Sinon

I have been on this for quite long and maybe I'm just missing something but my research did not yield any results that would help me.

So my question is:

If I have some code like this:

shell.on('message', function (message) {
// do something
});

And I want to test it as if it had been called with a certain message (or even an error), could I somehow do that with Sinon? ( just putting the do something in an external function will only work to some degree so I do hope for an answer that at least has a way to fake-call shell.on to test if the inner function gets invoked).

The "shell" is an instance of the shell of the npm Package "Python-Shell"

Maybe it's not possible at all or maybe I'm just blind but any help is much appreciated!

Upvotes: 0

Views: 468

Answers (1)

Mark
Mark

Reputation: 92440

The python-shell instance is instance of an EventEmitter. So you can cause the on handler to fire by just emitting the message:

var PythonShell = require('python-shell');

var pyshell = new PythonShell('my_script.py');

pyshell.on('message', function (message) {
    console.log("recieved", message);
});

pyshell.emit('message', "fake message?")
// writes: 'recieved fake message?'

You can also stub the instance with Sinon and call yields to call the callback:

const sinon = require('sinon')
var PythonShell = require('python-shell');

var pyshell = new PythonShell('my_script.py');
var stub = sinon.stub(pyshell, "on");
stub.yields("test message")
// writes received test message to console

pyshell.on('message', function (message) {
    console.log("received", message);
});

This might be more useful if you don't want to prevent the default behavior when running a test.

Upvotes: 2

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