How to spyOn a function which has an Promise inside and don't return the result but handles the response itself? - jasmine

Question

How can I spyOn a method called placed in the object?
// Game.js
export default {
mine: null,
handle: function(me) {
console.log(" FOOOOO " + me)
},
setSource: function() {
this.mine.getSource().then((response) => {
const {source} = response
this.handle(source)
})
}
}
Here i try to spy:
// GameSpec.js
import Game from '../../lib/jasmine_examples/Game'
Game.mine = {}
describe("Game", function() {
it("should set source and handle it", function() {
Game.mine.getSource = () => {
return new Promise((resolve)=>{
resolve( {
source : 'BAAAAR'
})
})
}
spyOn(Game, 'handle').and.callThrough()
Game.setSource()
expect(Game.handle).toHaveBeenCalled()
});
});
In the output you can see the function "handle" was called:
Started
F FOOOOO BAAAAR
Failures:
1) Game should set source and handle it
Message:
Expected spy handle to have been called.
Stack:
Error: Expected spy handle to have been called.
at <Jasmine>
at UserContext.<anonymous> (/Users/silverbook/Sites/zTest/jasmine/spec/jasmine_examples/PlayerSpec.js:20:29)
at <Jasmine>
1 spec, 1 failure
But jasmine says it was not called.
If i remove the mocked Promise the test passes but i needed there. In another test i will return an error in the Promise and let it handle from another function.
So the Promise breaks the test but why?

Answer 1

The test executes synchronously and the expect fails before the callback queued by this.mine.getSource().then() has a chance to execute.
For Jasmine >= 2.7 and async function support you can convert your test function into an async function and add an await Promise.resolve(); where you want to pause the synchronous test and let any queued callbacks execute.
For your test it would look like this:
import Game from '../../lib/jasmine_examples/Game'
Game.mine = {}
describe("Game", function() {
it("should set source and handle it", async () => {
Game.mine.getSource = () => {
return new Promise((resolve)=>{
resolve( {
source : 'BAAAAR'
})
})
}
spyOn(Game, 'handle').and.callThrough();
Game.setSource();
await Promise.resolve(); // let the event loop cycle
expect(Game.handle).toHaveBeenCalled();
});
});
For older (>= 2.0) Jasmine versions you can use done() like this:
import Game from '../../lib/jasmine_examples/Game'
Game.mine = {}
describe("Game", function() {
it("should set source and handle it", (done) => {
Game.mine.getSource = () => {
return new Promise((resolve)=>{
resolve( {
source : 'BAAAAR'
})
})
}
spyOn(Game, 'handle').and.callThrough();
Game.setSource();
Promise.resolve().then(() => {
expect(Game.handle).toHaveBeenCalled();
done();
});
});
});

Answer 2

You can run the test inside fakeAsync and run tick() before the expect()
Service:
getFirebaseDoc() {
this.db.firestore.doc('some-doc').get()
.then(this.getFirebaseDocThen)
.catch(this.getFirebaseDocCatch);
}
Unit testing:
it('should call getFirebaseDocThen', fakeAsync(() => { // note `fakeAsync`
spyOn(service, 'getFirebaseDocThen');
spyOn(service.db.firestore, 'doc').and.returnValue({
get: (): any => {
return new Promise((resolve: any, reject: any): any => {
return resolve({ exists: true });
});
},
});
service.getFirebaseDoc();
tick(); // note `tick()`
expect(service.getFirebaseDocThen).toHaveBeenCalled();
}));