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How to use jest.spyOn for a function (React)

How do I write a test for this function? I first tried to include an optional param in the function such as mockData and go from there, but that seems too tedious. I have a function, something like this:
export async function getBreadcrumbs(service, id) {
const { folderId, label } = await getFileDetailsById(id);
const { breadcrumbs } = await getFoldersService(service, folderId);
return [...breadcrumbs, { label, id: '' }];
}
I'm thinking jest.spyOn is what I need to write the test with but I'm not sure how to approach it. I started with:
import * as crumbs from '.....data'
describe('getCrumbs', () => {
it('should return breadcrumbs name and id', async () => {
const data = jest.spyOn(crumbs, 'getBreadcrumbs')
});
});
But I'm not sure where to go from here. How can I mock a return of this function? This function returns:
[{ displayName: 'Hey', id: '' }]
getFileDetailsById and getFoldersService are API calls.
TLDR: I have a function and I'm unsure how to mock its return.

How to create pages from non-seriazable data(functions)

I have this JavaScript data file(src/test/test.js):
module.exports = {
"title": "...",
"Number": "number1",
"Number2": ({ number1 }) => number1 / 2,
}
I want to pass this file verbatim(functions preserved) to a page, so that the page can use that data to build itself. I already have the page template and everything else sorted out, I just need to find a way to pass this into the page.
The first approach I tried is requireing this file in gatsby-node.js and then passing it as pageContext.
gatsby-node.js
const path = require('path');
exports.createPages = ({actions, graphql}) => {
const { createPage } = actions;
return graphql(`
query loadQuery {
allFile(filter: {sourceInstanceName: {eq: "test"}}) {
edges {
node {
relativePath
absolutePath
}
}
}
}
`).then(result => {
if (result.errors) {
throw result.errors;
}
for (const node of result.data.allFile.edges.map(e => e.node)) {
const data = require(node.absolutePath);
createPage({
path: node.relativePath,
component: path.resolve('./src/templates/test.js'),
context: data,
});
}
});
};
gatsby-config.js
module.exports = {
plugins: [
{
resolve: `gatsby-source-filesystem`,
options: {
name: `test`,
path: `${__dirname}/src/test/`,
},
},
],
}
src/templates/test.js
import React from 'react';
const index = ({ pageContext }) => (
<p>{pageContext.Number2()}</p>
);
export default index;
However, I get this warning when running the dev server:
warn Error persisting state: ({ number1 }) => number1 / 2 could not be cloned.
If I ignore it and try to use the function anyway, Gatsby crashes with this error:
WebpackError: TypeError: pageContext.Number2 is not a function
After searching for a while, I found this:
The pageContext was always serialized so it never worked to pass a function and hence this isn't a bug. We might have not failed before though.
- Gatsby#23675
which told me this approach wouldn't work.
How could I pass this data into a page? I've considered JSON instead, however, JSON can't contain functions.
I've also tried finding a way to register a JSX object directly, however I couldn't find a way.

Regarding the main topic, as you spotted, can't be done that way because the data is serialized.
How could I pass this data into a page? I've considered JSON instead,
however, JSON can't contain functions.
Well, this is partially true. You can always do something like:
{"function":{"arguments":"a,b,c","body":"return a*b+c;"}}
And then:
let func = new Function(function.arguments, function.body);
In this case, you are (de)serializing a JSON function, creating and casting a function based on JSON parameters. This approach may work in your scenario.
Regarding the JSX, I guess you can try something like:
for (const node of result.data.allFile.edges.map(e => e.node)) {
const data = require(node.absolutePath);
createPage({
path: node.relativePath,
component: path.resolve('./src/templates/test.js'),
context:{
someComponent: () => <h1>Hi!</h1>
},
});
}
And then:
import React from 'react';
const Index = ({ pageContext: { someComponent: SomeComponent} }) => (
return <div><SomeComponent /></div>
);
export default index;
Note: I don't know if it's a typo from the question but index should be capitalized as Index
In this case, you are aliasing the someComponent as SomeComponent, which is a valid React component.

Match object inside object in jest

I'm testing a function to see if, when called, it will return the proper created list.
To start, I create the elements, using the createDesign.execute() functions. It's tested on another file and working.
Then, I call the function I want to test: listAllDesigns.execute() and store it's value in a variable.
If I console.log(list), it returns the full list properly.
In pseudocode, what I'd like to do is: Expect list array to have an element with the design object and, within it, a design_id that equals "payload3".
How should I write this test?
Is there a better way to do this? (other than checking if list !== empty, please)
it('should return a list of all designs', async () => {
// Create fake payloads
const payload1 = {
...defaultPayload,
...{ design: { ...defaultPayload.design, design_id: 'payload1' } },
};
const payload2 = {
...defaultPayload,
...{ design: { ...defaultPayload.design, design_id: 'payload2' } },
};
const payload3 = {
...defaultPayload,
...{ design: { ...defaultPayload.design, design_id: 'payload3' } },
};
await createDesign.execute(payload1);
await createDesign.execute(payload2);
await createDesign.execute(payload3);
const list = await listAllDesigns.execute();
// expect(list). ????
});

The easiest method would be a combination of expect.arrayContaining and expect.objectContaining like so:
expect(list).toEqual(
expect.arrayContaining([
expect.objectContaining({
design: expect.objectContaining({
design_id: "payload3"
})
})
])
);

Jest Mock returns undefined instead of data

I'm trying to mock a function and not sure what i'm doing wrong here. I have this function "getGroups"
getGroups:
export const getGroups = async () => {
try {
const groupApiUrl = getDashboardPath(GROUPS_TAB_INDEX);
const data = await fetch(groupApiUrl, { cache: 'force-cache' });
const userData = await data.json();
return userData;
} catch (error) {
throw Error(error);
}
};
___mocks___/getGroups.js:
export default async () => {
return {
groups: [
{ id: 1, name: 'Data1' },
{ id: 2, name: 'Data2' }
]
};
};
getGroups.test.js:
jest.mock('./getGroups.js');
// eslint-disable-next-line import/first
import { getGroups } from './getGroups';
const fakeRespose = {
groups: [
{ id: 1, name: 'Data1' },
{ id: 2, name: 'Data2' }
]
};
describe('getGroups', () => {
it('returns data', async () => {
const data = await getGroups();
console.log('DATA', data); <---- UNDEFINED?
expect(data).toBeDefined();
expect(data).toMatchObject(fakeRespose);
});
it('handles error', async () => {
// const data = await getGroups();
await getGroups().toThrow('Failed');
});
});

What are you doing wrong here?
Default export in your mock instead of named as in the implementation
In your implementation you're using named export and you're importing { getGroups } so to make it work you need to change your mock like this
__mocks__\getGroups.js
export const getGroups = async () => {
return {
groups: [
{ id: 1, name: 'Data1' },
{ id: 2, name: 'Data2' }
]
};
};
working example
TL;DR
Testing mock
There is no point at all to test mock function. This does not proves your implementation is working. Even if you change your implementation your tests will still pass.
Use mocks only for the dependencies of your implementation
Use jest.genMockFromModule
It will create jest.fn() for each of the module's exported methods and will preserve the constants, allowing you to change the return value/implementation for some test cases and will also be able to write assertions if the function have been called
__mocks__\getGroups.js
const mock = jest.genMockFromModule('../getGroups');
mock.getGroups.mockResolvedValue({
groups: [
{ id: 1, name: 'Data1' },
{ id: 2, name: 'Data2' }
]
})
module.exports = mock;
Jest will automatically hoist jest.mock calls (read more...)
So you can safely leave the import statements first and then call jest.mock

From Jest Docs, here's an example of a Mock.
jest.mock('../moduleName', () => {
return jest.fn(() => 42);
});
// This runs the function specified as second argument to `jest.mock`.
const moduleName = require('../moduleName');
moduleName(); // Will return '42';
In your case data is undefined, because you haven't actually supplied a mocked implementation for the function or the mock hasn't worked and you're still calling the original function.
Example Reference: https://jestjs.io/docs/en/jest-object#jestmockmodulename-factory-options
However, in your simple case you could also solve this with a spy, either jest.spyOn or jest.fn(). Here are two solutions to what you're trying to achieve. You can look at the code and run it here: https://repl.it/repls/FairUnsungMice
UPDATE after comment:
Manual mocks are defined by writing a module in a __mocks__/
subdirectory immediately adjacent to the module. For example, to mock
a module called user in the models directory, create a file called
user.js and put it in the models/__mocks__ directory. Note that the
__mocks__ folder is case-sensitive, so naming the directory __MOCKS__ will break on some systems.
Double check the naming, directory structure & type of exports you've setup - they should match. Also, it's worth checking this out: https://github.com/facebook/jest/issues/6127 - looks like an open issue with jest. If you need a solution, look at using a different approach as I mentioned.
Reference: https://jestjs.io/docs/en/manual-mocks

My mutations aren't working! How do I correct this?

I am trying to set the breakfastMenu array in state as shown below but I can't see the array being filled in my vue-devtools.
I have properly set-up the Vuex methods and checked twice, also I didn't receive any sort of error. So, why do I have a logical error in my code?
store.js:
export default new Vuex.Store({
state: {
menu: [],
breakfastMenu: [],
lunchMenu: [],
dinnerMenu: []
},
mutations: {
'SET_MENU': (state, menuMaster) => {
state.menu = menuMaster;
},
'SET_BREAKFAST_MENU': (state, order) => {
state.breakfastMenu.unshift(order);
},
'SET_LUNCH_MENU': (state, order) => {
state.breakfastMenu.unshift(order);
},
'SET_DINNER_MENU': (state, order) => {
state.breakfastMenu.unshift(order);
},
},
actions: {
initMenu: ({ commit }, menuMaster) => {
commit('SET_MENU', menuMaster)
},
initBreakfastMenu: ({ commit, state }) => {
state.menu.forEach((element) => {
if (element.categoryId == 1) {
commit('SET_BREAKFAST_MENU', element)
}
});
},
initLunchMenu: ({ commit, state }) => {
state.menu.forEach((element) => {
if (element.categoryId == 2) {
commit('SET_LUNCH_MENU', element)
}
});
},
initDinnerMenu: ({ commit, state }) => {
state.menu.forEach((element) => {
if (element.categoryId == 3) {
commit('SET_DINNER_MENU', element)
}
});
},
},
getters: {
getBreakfastMenu(state) {
return state.breakfastMenu
},
getLunchMenu(state) {
return state.lunchMenu
},
getDinnerMenu(state) {
return state.dinnerMenu
},
}
})
Breakfast.vue:
import { mapActions, mapGetters } from 'vuex';
export default {
data() {
return {
breakfastArray: []
};
},
methods: {
...mapActions(['initBreakfastMenu']),
...mapGetters(['getBreakfastMenu']),
},
created() {
this.initBreakfastMenu;
this.breakfastArray = this.getBreakfastMenu;
}
};
No error messages so far!
I need the breakfastMenu array filled in store.js.
Please help out!

A few thoughts.
Firstly, this line:
this.initBreakfastMenu;
You aren't actually calling the method. It should be:
this.initBreakfastMenu();
Next problem is this:
...mapGetters(['getBreakfastMenu']),
The line itself is fine but it's inside your methods. It should be in the computed section.
You haven't included any sample data for state.menu but it's also worth noting that initBreakfastMenu won't do anything unless there is suitable data inside state.menu. I suggest adding some console logging to ensure that everything is working as expected there.
SET_BREAKFAST_MENU, SET_LUNCH_MENU and SET_DINNER_MENU are all modifying state.breakfastMenu. I would assume that this is incorrect and each should be modifying their respective menu.
I would also note that using local data for breakfastArray is suspicious. Generally you'd just want to use the store state directly via the computed property rather than referencing it via local data. This is not necessarily wrong, you may want to detach the component data from the store in this way, but keep in mind that both are referencing the same array so modification to one will also affect the other. You aren't taking a copy of the array, you're just creating a local reference to it.
You should also consider whether you actually need the 4 menu types within your state. If breakfastMenu, lunchMenu and dinnerMenu are all just derived from menu then you'd be better off just implementing those using getters. getters are the store equivalent of computed properties and can contain the relevant filtering logic to generate their value from state.menu.

initBreakfastMenu is an action and you may want to use this.initBreakfastMenu()