I'm writing some tests for a class. In my tests if I don't call browserViewPreload.init() the test fails, but when I do call browserViewPreload.init() it passes.
Why should I need to explicitly call browserViewPreload.init() in the test when I've already done it in my beforeEach block?
//myFile.ts
export default class BrowserViewPreload {
constructor(){
this.init();
}
attachMouse(){
console.log('attaching mouse')
}
init(){
return document.addEventListener('DOMContentLoaded', this.attachMouse)
}
}
//myFile.spec.ts
import BrowserViewPreload from './browserViewPreload'
function bootStrapComponent() {
return new BrowserViewPreload();
};
describe('BrowserViewPreload Class', () => {
var browserViewPreload;
let initSpy
let docspy
let mouseSpy
beforeEach(()=>{
browserViewPreload = bootStrapComponent();
initSpy = jest.spyOn(browserViewPreload, 'init')
docspy = jest.spyOn(document, 'addEventListener')
})
it('should report name', () => {
//browserViewPreload.init(); not including this makes the tests fail. Why do I need to make the call here when I've already done so in the beforeEach
expect(initSpy).toHaveBeenCalled();
expect(docspy).toHaveBeenCalled();
document.dispatchEvent(new Event('DOMContentLoaded'));
expect(mouseSpy).toHaveBeenCalled();
});
});
I guess it's because you are creating BrowserViewPreload object before attaching the initSpy to it.
Related
I want to test whether the main class method of getService return the correct new class based on the correct conditional
// main.js
import ServiceA from './serviceA'
import ServiceB from './serviceB'
class Main {
constructor(){}
getService(serviceName){
switch(serviceName){
case 'serviceA':
return new ServiceA()
case 'serviceB':
return new ServiceB()
default
return null
}
}
}
Would it be possible to test that the returned class is correct? I tried something like this
import Main from './Main'
describe('Main method', () => {
describe('getService given ServiceA', () => {
it.skip('should return an instantiate of ServiceA class', function () {
const main = new Main();
const getService = spy(main, 'getService');
main.getService('serviceA');
expect(getService).to.be.an.instanceOf(ServiceA);
});
});
There shouldn't be a need to spy on getService(). Since you are just testing the input and output of the getService() without any dependencies. Spying would allow to see call count and arguments passed to the spy to see if it was called inside the method you are testing. How you had it is mostly correct as it is.
import Main from './Main'
describe('Main method', () => {
describe('getService given ServiceA', () => {
it('should return an instantiate of ServiceA class', function () {
const main = new Main();
const result = main.getService('serviceA');
expect(result).to.be.an.instanceOf(ServiceA);
});
});
I have some code that has functions inside functions, and I want to be able to unit test the functions inside the parent function.
I am looking to have tests that unit test these and spy on them (both requirements are needed).
Example:
export default parentFunction = () => {
const innerFunction = () => {
//that does stuff
}
const anotherInnerFunction = () => {
//that does more stuff
}
//and at some point, the functions are called
//like this
innerFunction()
const anotherFunction = () => {
//or like this
anotherInnerFunction()
}
}
I have not been able to find a way to test these inner functions. I have tried the following.
Example test
import parentFunction from "myfile"
it("should call innerFunction", () => {
//this causes an error in jest
const innerFunctionSpy = jest.spyOn(parentFunction, "innerFunction")
//..etc
expect(innerFunctionSpy).toHaveBeenCalled()
})
it("will return a value from anotherInnerFunction", () => {
//this does not work
const value = parentFunction.anotherInnerFunction()
//this also does not work
const value = parentFunction().anotherInnerFunction()
//..etc
})
Does the parent function need to be refactored in order to be able to tests these inner functions? If my parent function was an object then I could test these, however, I am not sure if I can refactor my code to work like this.
For example
export default parentFunction = {
innerFunction: () => {
//that does stuff
},
//more code
}
You cannot access the variables or functions scoped inside another function in JavaScript. Unless you explicitly expose them by returning them from that function or export them from the module. This is not about Jest, this is how it works in JavaScript.
jest.spyOn(parentFunction, "innerFunction")
The above line of code indicates to Jest that the innerFunction function is set as a property of the parentFunction object but that is not the case. In fact innerFunction is a function scoped inside the parentFunction which cannot be accessed from outside of the scope of parentFunction. Unless you return it explicitly or define it on the module level scope and then export it.
But the inner workings or the implementation details of such inner functions should not be exposed, but if it is needed it should be marked as such using an _ before its name, take the following example:
//scoped to the module
const _innerFunction = () => {
//that does stuff
}
//scoped to the module
const _anotherInnerFunction = () => {
//that does more stuff
}
//exported as a public API
const anotherFunction = () => {
_anotherInnerFunction()
}
const publicApi = {
anotherFunction,
// expose the private functions for unit tests
_innerFunction,
_anotherInnerFunction
}
export default publicApi;
Then in your Jest test case:
import publicApi from "myfile"
it("should call anotherFunction", () => {
const anotherFunctionSpy = jest.spyOn(publicApi, "anotherFunction")
//..etc
expect(anotherFunctionSpy ).toHaveBeenCalled()
})
it("should call _innerFunction", () => {
const innerFunctionSpy = jest.spyOn(publicApi, "_innerFunction")
//..etc
expect(innerFunctionSpy ).toHaveBeenCalled()
})
I need to spyOn a method of an object created dynamically inside another method
So consider the following:
public doStuff = () => {
const myThing = new MyThing();
myThing.doSomethingElse().then((data) => {
//do more stuff here...
})
}
I want to therefore spyOn the instance of MyThing and the call to doSomethingElse().
I did come across a solution here which make use of the object's prototype, which I attempted like so
spyOn(MyThing.prototype, 'doSomethingElse').and.returnValue(Promise.resolve({foo: 'bar'}));
But this does not work after I call doStuff() in my tests, I get an error:
Error: : doSomethingElse() method does not exist
But I know this method is fine, since it runs as expected locally.
I am unsure how to proceed, can anyone assist?
Thanks
You might be missing something in your test. This is a simple test and you can see it works as you expected
require("jasmine");
class MyThing {
async doSomethingElse() {
return { bar: "foo" };
}
}
class Stuff {
doStuff() {
const myThing = new MyThing();
myThing.doSomethingElse().then(data => {
console.log(data);
});
}
}
describe("doSomethingElse", () => {
it("toHaveBeenCalled", () => {
spyOn(MyThing.prototype, "doSomethingElse").and.returnValue(
Promise.resolve({ foo: "bar123" })
);
const stuff = new Stuff();
stuff.doStuff();
expect(MyThing.prototype.doSomethingElse).toHaveBeenCalled();
});
});
The key is to use the spyOn before you instantiate the class that contains the doStuff function. If we move the const stuff = new Stuff(); above the spyOn it fails.
Hope it helps
You can create a spy object with mock method by passing in an object where the property names represent returned data for methods.
describe('test', () => {
let mock;
beforeEach(() => {
mock = jasmine.createSpyObj('mock', {
doSomethingElse: Promise.resolve({foo: 'bar'})
});
});
it('call mock', async () => {
const result = await mock.doSomethingElse();
expect(result.foo).toEqual('bar');
});
});
<link href="https://cdnjs.cloudflare.com/ajax/libs/jasmine/3.4.0/jasmine.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jasmine/3.4.0/jasmine.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jasmine/3.4.0/jasmine-html.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jasmine/3.4.0/boot.js"></script>
I'm trying to set a unit testing boilerplate for my company. Our front end projects are built with ES6 classes and have a dependency to our core product. The front end code gets wrapped through a build process in a whole other block of code that is basically a closure and captures the dependency. So we don't have to manually import it in order to use it.
Let's say the dependency is called productScope and it's an object that has some DOM models, internal APIs and parameters among many other things necessary for each project. At the moment, Mocha throws ReferenceError: productScope is not defined. How can I mock this object? Or should I just use the actual object?
Example:
class someClass {
constructor() {
const id = productScope.items[0].id
const item = productScope.domModel.querySelector('.some-div')
item.classList.add(`added-${id}`)
}
}
This get wrapped in core code like below:
(function(productScope) {
// front end code goes here
}(productScope)
Testing file:
import someClass from '../../js/someClass'
describe('someClass', function() {
const someClass = new someClass()
it('should be a class', function() {
console.log(someClass)
});
});
You can try something like this
describe('#someClass', () => {
let someClass;
beforeEach(() => {
global.productScope = {
// mocking productScope object
};
});
it('should be a class', () => {
someClass = new SomeClass;
console.log(someClass);
});
afterEach(() => {
delete global.productScope;
});
});
or alternatively if you want more specific mock logic for each test case
describe('#someClass', () => {
let someClass;
it('should be a class', () => {
global.productScope = {
// mocking productScope object
};
// Test logic start
someClass = new SomeClass;
console.log(someClass);
// Test logic end
delete global.productScope;
});
});
Looks like productScope is a global variable.
Something like this should work for you.
import someClass from '../../js/someClass';
describe('someClass', function() {
let someClass;
beforeEach(() => {
global.productScope = {
// you mock definition
someClass = new someClass();
};
});
it('should be a class', function() {
console.log(someClass)
});
});
I'm with other answers as well, as managing global variables seems to be the simplest and most straightforward solution.
However, you can use toString to get class's string representation, and eval it to bind to closure's scope:
class someClass {
constructor() {
this.id = scopedId
}
}
// pass class as an argument
function scopeFactory(classDef) {
// define scoped data
let scopedId = 2;
// eval is used to bind class to the local closure
// so `scopedId` will be in charge
return eval("(" + classDef + ")");
}
const scopedSomeClass = scopeFactory(someClass);
console.log(new scopedSomeClass)
Note that eval(someCLass.toString()) doesn't work without parentheses.
You can add it as a helper function, into your project.
I have the following hypothetical scenario:
// file MyClass.js in an external package
class MyClass {
myfunc = () => {
// do something
}
}
// file in my project
function myFunctionToBeTested() {
const instance = new MyClass()
instance.myFunc()
}
I need to create a test with Jest that makes sure instance.myFunc was called
One of the option is to replace MyClass module with mock implementation
const mockmyfunc = jest.fn()
jest.mock("path/to/external/package/MyClass", () => {
return jest.fn().mockImplementation(() => {
return {myfunc: mockmyfunc}
})
})
And then write following test
it("Test myfunc called in functionToBeTested", () => {
functionToBeTested()
expect(mockmyfunc).toHaveBeenCalled()
})
Note that this is not the only way, you can dive into https://facebook.github.io/jest/docs/en/es6-class-mocks.html for other alternatives.
Update
If the myfunc would be an actual function (which i guess is not an option since it's external package?)
export class MyClass {
myFunc() {
// do smth
}
}
and you would not need to replace the implementation, you could be using jest's automock
import MyClass from "path/to/external/package/MyClass"
jest.mock("path/to/external/package/MyClass")
it("Test myfunc called in functionToBeTested", () => {
functionToBeTested()
const mockMyFunc = MyClass.mock.instances[0].myFunc
expect(mockMyFunc).toHaveBeenCalled()
})
you can mock out the class and assign the default export of that file to a variable as follows:
jest.mock('../../utils/api/api');
const FakeClass = require('../someFile.js').default;
then access calls to a function on your mock class like this:
FakeClass.prototype.myFunc.mock.calls