CODEWITHSUNDEEP
javascriptnode.jstestingjestjs
Jaredcheeda
Jaredcheeda

Reputation: 2014

Mocking execSync in Jest

How do I mock out executing a child process in Jest

const execSync = require('child_process').execSync;
//...
expect(execSync)
  .toHaveBeenCalledWith('npm install');

But not actually have it run the npm install during the test.

Upvotes: 2

Views: 3869

Answers (2)

felixmosh
felixmosh

Reputation: 35513

You can use lib mock with __mocks__ folder that will hold child_process folder which will be loaded by jest automatically.

Just create a file 

// __mocks__/child_process/index.js

module.exports = {
  execSync: jest.fn()
};

that will export a mock implementation of child_process.

Upvotes: 0

Sebastian Southern
Sebastian Southern

Reputation: 21

Can just do something like the following:

jest.mock("child_process", () => {
  return {
    execSync: () => "This is a test message"
  };
});

Where the return value can be a number, string, object or whatever. It just allows you to override the actual implementation of execsync.

Upvotes: 2

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