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 a function that returns true or false, lets call it myFunc
myFunc (){
if(something){return true}
else{return false}
}
that's what it does for sake of arg
I then call it somewhere else
if(myFunc()){
}else{
}
when I log it out, it continually comes out as false. however, when i have mocked it in my test like so:
const myMock = (myModule.myFunc = jest.fn())
myMock.mockReturnValue(true)
so why is it still coming back as false when I log it from the index file? or is that not quite how mocking works?
I'm guessing that myModule is the object you imported, and then you set the mock function on that object. But in the myModule file you are referencing that function directly, not through a module reference, right?
The proper way would probably be to move myFunc out of myModule. But if you want to keep it there, then you are going to have to partially mock myModule:
jest.mock('./myModule', () => {
return {
...jest.requireActual('./myModule'),
myFunc: jest.fn()
}
})
But seriously consider moving myFunc out of myModule, because partial mocking is difficult and confusing.
One way I found to solve my issue was to use a class instead.
Here is a sudo example:
Implementation
export class Location {
getLocation() {
const environment = this.getEnvironmentVariable();
return environment === "1" ? "USA" : "GLOBAL";
}
getEnvironmentVariable() {
return process.env.REACT_APP_LOCATION;
}
}
Test
import { Location } from "./config";
test('location', () => {
const config = new Location();
jest.spyOn(config, "getEnvironmentVariable").mockReturnValue("1")
const location = config.getLocation();
expect(location).toBe("USA");
});
Can somebody help me with manual mocking in Jest, please? :)
I try to have Jest use the mock instead of the actual module.
my test:
// __tests__/mockTest.js
import ModuleA from "../src/ModuleA"
describe("ModuleA", () => {
beforeEach(() => {
jest.mock("../src/ModuleA")
})
it("should return the mock name", () => {
const name = ModuleA.getModuleName()
expect(name).toBe("mockModuleA")
})
})
my code:
// src/ModuleA.js
export default {
getModuleName: () => "moduleA"
}
// src/__mocks__/ModuleA.js
export default {
getModuleName: () => "mockModuleA"
}
I think I followed everything the documentation says about manual mocks, but perhaps I'm overlooking something here?
This is my result:
Expected value to be:
"mockModuleA"
Received:
"moduleA"
Module mocks are hoisted when possible with babel-jest transform, so this will result in mocked module:
import ModuleA from "../src/ModuleA"
jest.mock("../src/ModuleA") // hoisted to be evaluated prior to import
This won't work if a module should be mocked per test basis, because jest.mock resides in beforeEach function.
In this case require should be used:
describe("ModuleA", () => {
beforeEach(() => {
jest.mock("../src/ModuleA")
})
it("should return the mock name", () => {
const ModuleA = require("../src/ModuleA").default;
const name = ModuleA.getModuleName()
expect(name).toBe("mockModuleA")
})
})
Since it's not an export but a method in default export that should be mocked, this can also be achieved by mocking ModuleA.getModuleName instead of entire module.
This answer is not strictly related to the OPs question but google lead me here for a similar issue where jest.mock('module', () => ({})) in the root of a file did not work. In my case it was caused by cyclic dependencies. So if jest suddenly starts to ignore calls to jest.mock() then you might want to check for cyclic dependencies in your files.
When testing a module that has a dependency in a different file and assigning that module to be a jest.mock, TypeScript gives an error that the method mockReturnThisOnce (or any other jest.mock method) does not exist on the dependency, this is because it is previously typed.
What is the proper way to get TypeScript to inherit the types from jest.mock?
Here is a quick example.
Dependency
const myDep = (name: string) => name;
export default myDep;
test.ts
import * as dep from '../depenendency';
jest.mock('../dependency');
it('should do what I need', () => {
//this throws ts error
// Property mockReturnValueOnce does not exist on type (name: string)....
dep.default.mockReturnValueOnce('return')
}
I feel like this is a very common use case and not sure how to properly type this.
You can use type casting and your test.ts should look like this:
import * as dep from '../dependency';
jest.mock('../dependency');
const mockedDependency = <jest.Mock<typeof dep.default>>dep.default;
it('should do what I need', () => {
//this throws ts error
// Property mockReturnValueOnce does not exist on type (name: string)....
mockedDependency.mockReturnValueOnce('return');
});
TS transpiler is not aware that jest.mock('../dependency'); changes type of dep thus you have to use type casting. As imported dep is not a type definition you have to get its type with typeof dep.default.
Here are some other useful patterns I've found during my work with Jest and TS
When imported element is a class then you don't have to use typeof for example:
import { SomeClass } from './SomeClass';
jest.mock('./SomeClass');
const mockedClass = <jest.Mock<SomeClass>>SomeClass;
This solution is also useful when you have to mock some node native modules:
import { existsSync } from 'fs';
jest.mock('fs');
const mockedExistsSync = <jest.Mock<typeof existsSync>>existsSync;
In case you don't want to use jest automatic mock and prefer create manual one
import TestedClass from './TestedClass';
import TestedClassDependency from './TestedClassDependency';
const testedClassDependencyMock = jest.fn<TestedClassDependency>(() => ({
// implementation
}));
it('Should throw an error when calling playSomethingCool', () => {
const testedClass = new TestedClass(testedClassDependencyMock());
});
testedClassDependencyMock() creates mocked object instance
TestedClassDependency can be either class or type or interface
Use the mocked helper
like explained here
// foo.spec.ts
import { foo } from './foo'
jest.mock('./foo')
// here the whole foo var is mocked deeply
const mockedFoo = jest.mocked(foo, true)
test('deep', () => {
// there will be no TS error here, and you'll have completion in modern IDEs
mockedFoo.a.b.c.hello('me')
// same here
expect(mockedFoo.a.b.c.hello.mock.calls).toHaveLength(1)
})
test('direct', () => {
foo.name()
// here only foo.name is mocked (or its methods if it's an object)
expect(jest.mocked(foo.name).mock.calls).toHaveLength(1)
})
There are two solutions tested for TypeScript version 3.x and 4.x, both are casting desired function
1) Use jest.MockedFunction
import * as dep from './dependency';
jest.mock('./dependency');
const mockMyFunction = dep.myFunction as jest.MockedFunction<typeof dep.myFunction>;
2) Use jest.Mock
import * as dep from './dependency';
jest.mock('./dependency');
const mockMyFunction = dep.default as jest.Mock;
There is no difference between these two solutions. The second one is shorter and I would therefore suggest using that one.
Both casting solutions allows to call any jest mock function on mockMyFunction like mockReturnValue or mockResolvedValue
https://jestjs.io/docs/en/mock-function-api.html
mockMyFunction.mockReturnValue('value');
mockMyFunction can be used normally for expect
expect(mockMyFunction).toHaveBeenCalledTimes(1);
I use the pattern from #types/jest/index.d.ts just above the type def for Mocked (line 515):
import { Api } from "../api";
jest.mock("../api");
const myApi: jest.Mocked<Api> = new Api() as any;
myApi.myApiMethod.mockImplementation(() => "test");
Cast as jest.Mock
Simply casting the function to jest.Mock should do the trick:
(dep.default as jest.Mock).mockReturnValueOnce('return')
Use as jest.Mock and nothing else
The most concise way of mocking a module exported as default in ts-jest that I can think of really boils down to casting the module as jest.Mock.
Code:
import myDep from '../dependency' // No `* as` here
jest.mock('../dependency')
it('does what I need', () => {
// Only diff with pure JavaScript is the presence of `as jest.Mock`
(myDep as jest.Mock).mockReturnValueOnce('return')
// Call function that calls the mocked module here
// Notice there's no reference to `.default` below
expect(myDep).toHaveBeenCalled()
})
Benefits:
does not require referring to the default property anywhere in the test code - you reference the actual exported function name instead,
you can use the same technique for mocking named exports,
no * as in the import statement,
no complex casting using the typeof keyword,
no extra dependencies like mocked.
The latest jest allows you to do this very easily with jest.mocked
import * as dep from '../dependency';
jest.mock('../dependency');
const mockedDependency = jest.mocked(dep);
it('should do what I need', () => {
mockedDependency.mockReturnValueOnce('return');
});
Here's what I did with jest#24.8.0 and ts-jest#24.0.2:
source:
class OAuth {
static isLogIn() {
// return true/false;
}
static getOAuthService() {
// ...
}
}
test:
import { OAuth } from '../src/to/the/OAuth'
jest.mock('../src/utils/OAuth', () => ({
OAuth: class {
public static getOAuthService() {
return {
getAuthorizationUrl() {
return '';
}
};
}
}
}));
describe('createMeeting', () => {
test('should call conferenceLoginBuild when not login', () => {
OAuth.isLogIn = jest.fn().mockImplementationOnce(() => {
return false;
});
// Other tests
});
});
This is how to mock a non-default class and it's static methods:
jest.mock('../src/to/the/OAuth', () => ({
OAuth: class {
public static getOAuthService() {
return {
getAuthorizationUrl() {
return '';
}
};
}
}
}));
Here should be some type conversion from the type of your class to jest.MockedClass or something like that. But it always ends up with errors. So I just used it directly, and it worked.
test('Some test', () => {
OAuth.isLogIn = jest.fn().mockImplementationOnce(() => {
return false;
});
});
But, if it's a function, you can mock it and do the type conversation.
jest.mock('../src/to/the/Conference', () => ({
conferenceSuccessDataBuild: jest.fn(),
conferenceLoginBuild: jest.fn()
}));
const mockedConferenceLoginBuild = conferenceLoginBuild as
jest.MockedFunction<
typeof conferenceLoginBuild
>;
const mockedConferenceSuccessDataBuild = conferenceSuccessDataBuild as
jest.MockedFunction<
typeof conferenceSuccessDataBuild
>;
As of Jest 24.9.0 here is how you can mock and correctly type both your Class/Object/function and Jest properties.
jest.MockedFunction
jest.MockedClass
What we would like for a typed mock is that the mocked object type contains the union of the mocked object type and the type of Jest mocks.
import foo from 'foo';
jest.mock('foo');
const mockedFoo = foo as jest.MockedFunction<typeof foo>;
// or: const mockedFooClass = foo as jest.MockedClass<typeof FooClass>;
mockedFoo.mockResolvedValue('mockResult');
// Or:
(mockedFoo.getSomething as jest.MockedFunction<typeof mockedFoo.getSomething>).mockResolvedValue('mockResult');
As you can see, you can either manually cast what you need or you'll need something to traverse all foo's properties/methods to type/cast everything.
To do that (deep mock types) you can use jest.mocked() introduced in Jest 27.4.0
import foo from 'foo';
jest.mock('foo');
const mockedFoo = jest.mocked(foo, true);
mockedFoo.mockImplementation() // correctly typed
mockedFoo.getSomething.mockImplementation() // also correctly typed
I have found this in #types/jest:
/**
* Wrap a function with mock definitions
*
* #example
*
* import { myFunction } from "./library";
* jest.mock("./library");
*
* const mockMyFunction = myFunction as jest.MockedFunction<typeof myFunction>;
* expect(mockMyFunction.mock.calls[0][0]).toBe(42);
*/
Note: When you do const mockMyFunction = myFunction and then something like mockFunction.mockReturnValue('foo'), you're a changing myFunction as well.
Source: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/jest/index.d.ts#L1089
The top rated solution by Artur Górski does not work with the last TS and Jest.
Use MockedClass
import SoundPlayer from '../sound-player';
jest.mock('../sound-player'); // SoundPlayer is now a mock constructor
const SoundPlayerMock = SoundPlayer as jest.MockedClass<typeof SoundPlayer>;
A recent library solves this problem with a babel plugin: https://github.com/userlike/joke
Example:
import { mock, mockSome } from 'userlike/joke';
const dep = mock(import('./dependency'));
// You can partially mock a module too, completely typesafe!
// thisIsAMock has mock related methods
// thisIsReal does not have mock related methods
const { thisIsAMock, thisIsReal } = mockSome(import('./dependency2'), () => ({
thisIsAMock: jest.fn()
}));
it('should do what I need', () => {
dep.mockReturnValueOnce('return');
}
Be aware that dep and mockReturnValueOnce are fully type safe. On top, tsserver is aware that depencency was imported and was assigned to dep so all automatic refactorings that tsserver supports will work too.
Note: I maintain the library.
This is ugly, and in fact getting away from this ugliness is why I even looked at this question, but to get strong typing from a module mock, you can do something like this:
const myDep = (require('./dependency') as import('./__mocks__/dependency')).default;
jest.mock('./dependency');
Make sure you require './dependency' rather than the mock directly, or you will get two different instantiations.
For me this was enough:
let itemQ: queueItemType
jest.mock('../dependency/queue', () => {
return {
add: async (item: queueItemType, ..._args: any) => {
// then we can use the item that would be pushed to the queue in our tests
itemQ = item
return new Promise(resolve => {
resolve('Mocked')
})
},
}
})
Then, whenever the add method is called it will execute this code above instead of pushing it to the queue, in this case.
With TypeScript 2.8 we can do like this with ReturnType:
import * as dep from "./depenendency"
jest.mock("./dependency")
const mockedDependency = <jest.Mock<ReturnType<typeof dep.default>>>dep.default
it("should do what I need", () => {
mockedDependency.mockReturnValueOnce("return")
})
I have a react component(this is simplified in order to demonstrate the issue):
class MyComponent extends Component {
handleNameInput = (value) => {
this.searchDish(value);
};
searchDish = (value) => {
//Do something
}
render() {
return(<div></div>)
}
}
Now I want to test that handleNameInput() calls searchDish with the provided value.
In order to do this I would like to create a jest mock function that replaces the component method.
Here is my test case so far:
it('handleNameInput', () => {
let wrapper = shallow(<MyComponent/>);
wrapper.searchDish = jest.fn();
wrapper.instance().handleNameInput('BoB');
expect(wrapper.searchDish).toBeCalledWith('BoB');
})
But all I get in the console is SyntaxError:
SyntaxError
at XMLHttpRequest.open (node_modules/jsdom/lib/jsdom/living/xmlhttprequest.js:458:15)
at run_xhr (node_modules/browser-request/index.js:215:7)
at request (node_modules/browser-request/index.js:179:10)
at DishAdmin._this.searchDish (src/main/react/components/DishAdmin.js:155:68)
at DishAdmin._this.handleNameInput (src/main/react/components/DishAdmin.js:94:45)
at Object.<anonymous> (src/main/react/tests/DishAdmin.test.js:122:24)
So my question is, how do I properly mock component methods with enzyme?
The method can be mocked in this way:
it('handleNameInput', () => {
let wrapper = shallow(<MyComponent/>);
wrapper.instance().searchDish = jest.fn();
wrapper.update();
wrapper.instance().handleNameInput('BoB');
expect(wrapper.instance().searchDish).toBeCalledWith('BoB');
})
You also need to call .update on the wrapper of the tested component in order to register the mock function properly.
The syntax error was coming from the wrong assingment (you need to assign the method to the instance). My other problems were coming from not calling .update() after mocking the method.
Needs to be replaced wrapper.update(); with wrapper.instance().forceUpdate();
#Miha's answer worked with a small change:
it('handleNameInput', () => {
let wrapper = shallow(<MyComponent/>);
const searchDishMock = jest.fn();
wrapper.instance().searchDish = searchDishMock;
wrapper.update();
wrapper.instance().handleNameInput('BoB');
expect(searchDishMock).toBeCalledWith('BoB');
})