在 Jest 中模拟 execSync

Question

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.

Answer 1

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.

Answer 2

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 .