I am contributing to a project which is built with React (with webpack) running in Electron. When executing unit tests with Jest, it fails with the error TypeError: Cannot read property 'on' of undefined
(and works fine when not testing, eg. run with Electron).
The code:
import React, { Component } from 'react';
import { ipcRenderer } from 'electron';
// some more imports
class Setup extends Component {
constructor(props) {
super(props);
this.state = {
// some state
};
ipcRenderer.on('open-file-reply', this.someMethod); // << fails on this line
}
// more class stuff
}
It took me a few days but finally, I found this answer in this great blog post. Quote:
Jest is called from Node and doesn't run test code through Webpack. Instead, we have to use Jest's mocking functions to replace the import with a stub file.
Jest has a helper method called moduleNameMapper [object<string, string>]
. From jest documentation:
A map from regular expressions to module names that allow to stub out resources, like images or styles with a single module.
It should be added in your package.json root object like this:
{
"name": "My awesome app",
"jest": {
"moduleNameMapper": {
"electron": "<rootDir>/src/components/tests/mock/electron.js"
}
}
}
and the mock file itself (/src/components/tests/mock/electron.js):
export const ipcRenderer = {
on: jest.fn()
};
This way you can stub other electron modules and methods (like remote which is shown in the blog above).
Another way is creating an electron.js
file in __mocks__
in your root folder.
The electron.js should look something like
export const ipcRenderer = {
on: jest.fn(),
};
You can read more at https://jestjs.io/docs/en/manual-mocks#mocking-node-modules
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