Develop Reference

Test if an actual function was called with Jest

I am simply trying to test if a function was called using jest 26.6.3. I do not want to mock the implementation of the function. I want to test if my actual function was called.
const add = (a,b) => a + b;
test("add() was called", () => {
add(1,2);
expect(add).toHaveBeenCalled();
})
If I create a mock function, I don't understand how that would be testing to see if my REAL function has been invoked. Obviously, the mock function will be executed if I create it using jest.fn() and then invoke it. Would I have to spy on my add function? Still missing the fundamental understanding to do this simple task.

You will need to spy the function add to get some infos about her like when its called... Then you are to be able to do the expect.
You can do this with jest.spyOn.

Understanding Sinon Spies: What happens when a spy-wrapped method is called?

When I wrap the method of a class into a Sinon-spy like this:
sinon.spy(myObject, "myMethod")
What happens within the spy?
I guess the spy-object has a reference which points to "myObject.myMethod".
What happens when the method becomes call?
I know that the spy logs information about the invocation like times of invocations, the used parameter etc.
But does the myMethod really become invoked?
I mean: Passes the spy object the invocation further? Does the spy-object act as proxy? Or does it only log the information?

From a simple test it seems that sinon spy does call the original method:
it('does a thing', function() {
const el = {};
el.thing = function() { console.log('thing'); }
sinon.spy(el, 'thing');
el.thing();
console.log(el.thing.called);
});
// prints:
// thing
// true
It also seems like that from the docs:
sinon.spy(object, "method") creates a spy that wraps the existing function object.method. The spy will behave exactly like the original method (including when used as a constructor), but you will have access to data about all calls.

Calling helper functions from within template.rendered in Meteor.js, error in 1.0, fine in 0.9.3

In an effort to avoid repeating code I found it useful to have helper functions that could be called from within a foo.rendered function (for instance). Why is this possible in 0.9.3 of Meteor, but throws an error in 1.0 ?
Template.foo.helpers({
'fooFn' : function(){
return "something"
}
});
Template.foo.rendered = function(){
var something = Template.foo.fooFn();
}
Should I change the syntax in foo.rendered (am I calling it wrong?) or maybe use a different approach entirely (set up functions outside of the helpers({}) and rendered() and call those? or set this up as a registered helper function?

It looks like it is possible as of Meteor 1.0.3.1 to find and call helper functions, although it is clear it's not supposed to be used like this.
Still it can be done:
Template.foo.__helpers[" fooFn"]()
Please notice the leading space for the function name.
The other way of dealing with this is attaching a function to a global namespace, then calling that from somewhere else in your code, as user3557327 mentioned.
Additionally you can use:
Template.registerHelper('myHelper', function (){return 'Look At Me!'})
to register a global helper, and call it explicitly using:
UI._globalHelpers['myHelper']()

I think this would be a better method: How to use Meteor methods inside of a template helper
Define a function and attach it to the template. Call that function from rendered, as well as your template helper. Like MrMowgli said, you probably aren't "supposed" to call template helpers from within the .js file, only from the ...that could probably break in the future.
For example define a function and attach it to the tamplate:
Template.Play.randomScenario = function () { // HACK HACK HACK }
and then call it from your lifecycle method
Template.Play.created = function () {
Template.Play.randomScenario();
};
scenario: function () {
return Template.Play.randomScenario();;
},
I had the same problem and this is the solution I used. Hope that helps.

Jasmine spies callThrough and callFake

I have a scenario whereby I want to call done() on a beforeEach after a callback has been invoked.
I tried to do this as follows :
spyOn(scope, 'onAdmin').and.callThrough().and.callFake(function(){done()})
But I'm not sure I get the right behaviour. Essentially what I want to achieve is to be able to call done() after each callback is done doing what it does.
UPDATE: workaround solution
scope.onAdminBackup = scope.onAdmin;
spyOn(scope, 'onAdmin').and.callFake(function(admin) {
scope.onAdminBackup();
done() ;
})

I have never chained these kinds of functions together cuz in my mind they seem to do the opposite. You are saying when I call this method -onAdmin - in the scope call it as normal. Which is what the callThrough method jasmine provides for us does.
But then you are chaining along a callFake method as well so then you say but dont actually call it call this fake function instead - very conflicting.
If you want to call spy on the method onAdmin and instead of it being fired you want it to do something else - something mocked - then use the .and.callFake(fn). Also take into account like #stefan above said - dont invoke the function - callFake is simply wanting a function as a parameter it will take care of calling it itself.
This might be more along the lines of what you are looking for, if not show us some more code.
spyOn(scope, 'onAdmin')and.callFake(done)

you are calling done right-away when you write done()
try passing in done as a value:
spyOn(scope, 'onAdmin').and.callThrough().and.callFake(done)

I found a work around way to do this. Jasmine has a method called addSpyStategy where you can add a custom strategy like callThrough or callFake. It would look something like this:
jasmine.addSpyStrategy('callThroughAndThen', (spy, fn) => {
return function() {
spy.and.callThrough();
setTimeout(() => fn(...arguments), 0);
}
});
the timeout makes sure the real function finishes before executing the custom function. Then for your spy, you can do this:
const spy = spyOn(scope, 'onAdmin')
spy.and.callThroughAndThen(spy, () => {
// your custom callback
done();
});
note: make sure to put custom strategy in a beforeEach block

Testing delegate callbacks using Jasmine (JavaScript)

I have a simple JavaScript function that uses two delegates to (asynchronously) get one value back:
function getMyUserName() {
context.load(user);
context.executeQueryAsync(onGetMyUserNameSuccess, onGetMyUserNameFail);
}
function onGetMyUserNameSuccess() {
return user.get_title();
}
function onGetMyUserNameFail(sender, args) {
return args.get_message();
}
The "context" and "user" variables are already set and initialized, and the first delegate ("onGetMyUserNameSuccess") is getting the correct answer. The question is how I can test the "getMyUserName" function with Jasmine?. If I use "runs", I have no way to know the response from the delegates (also I don't see any way to know if the delegates are called). I tried to set spies to mock the delegates, but probably I didn't it correctly (I'm just starting with Jasmine).
Any help will be very welcome.
Thanks in advance,
Gustavo

In most of the cases when you have to work with async code, you should call the function by yourself. But not directly but in the way your code would call it. So in your case spy on context.executeQueryAsync and use spy.mostRecentCall.args to get the reference to the function and then call them.
var async = jasmin.spyOn(context, 'executeQueryAsync');
async.mostRecentCall.args[0]()
var args = {get_message: jasmine.createSpy()}
async.mostRecentCall.args[1]({}, args);
expect(args.get_message.toHaveBeenCalled());
Note that there is the sinon framework that have a bunch of methodes to automatically call callbacks