jest-mock-process

Easily mock NodeJS process properties in Jest.

Installation

npm install --save-dev jest-mock-process

Usage

JavaScript

var mockProcess = require('jest-mock-process');

var mockExit = mockProcess.mockProcessExit();
process.exit(1);
expect(mockExit).toHaveBeenCalledWith(1);
mockExit = mockProcess.mockProcessExit(new Error('Mock'));
expect(() => process.exit(0)).toThrowError('Mock');

var mockStdout = mockProcess.mockProcessStdout();
process.stdout.write('Hello, world!');
expect(mockStdout).toHaveBeenCalledWith('Hello, world!');

var mockStderr = mockProcess.mockProcessStderr();
process.stderr.write('Error');
expect(mockStderr).toHaveBeenCalledWith('Error');

var mockLog = mockProcess.mockConsoleLog();
console.log('Browser log');
expect(mockLog).toHaveBeenCalledWith('Browser log');

mockExit.mockRestore();
mockStdout.mockRestore();
mockStderr.mockRestore();
mockLog.mockRestore();

TypeScript

import { mockProcessExit, mockProcessStdout, mockProcessStderr, mockConsoleLog } from 'jest-mock-process';

let mockExit = mockProcessExit();
process.exit(1);
expect(mockExit).toHaveBeenCalledWith(1);
mockExit = mockProcessExit(new Error('Mock'));
expect(() => process.exit(0)).toThrowError('Mock');

const mockStdout = mockProcessStdout();
process.stdout.write('Hello, world!');
expect(mockStdout).toHaveBeenCalledWith('Hello, world!');

const mockStderr = mockProcessStderr();
process.stderr.write('Error');
expect(mockStderr).toHaveBeenCalledWith('Error');

const mockLog = mockConsoleLog();
console.log('Browser log');
expect(mockLog).toHaveBeenCalledWith('Browser log');

mockExit.mockRestore();
mockStdout.mockRestore();
mockStderr.mockRestore();
mockLog.mockRestore();

Advanced usage

• You can use mockedRun (or asyncMockedRun) to set-up a virtual environment that will automatically create and restore provided mocks:

import { mockedRun, MockedRunResult } from 'jest-mock-process';

const mockRun: (_: () => any) => MockedRunResult = mockedRun({
    stdout: mockProcessStdout,
    stderr: mockProcessStderr,
    exit: mockProcessExit,
    log: mockConsoleLog,
});
const mocks: MockedRunResult = mockRun(() => {
    process.stdout.write('stdout payload');
    process.stderr.write('stderr payload');
    process.exit(-1);
    console.log('log payload');
});
expect(mocks.stdout).toHaveBeenCalledTimes(1);
expect(mocks.log).toHaveBeenCalledWith('log payload');

• You can mock generic methods not supported by default in jest-mock-process with the spyOnImplementing function:

import { spyOnImplementing } from 'jest-mock-process';

const mockStdin = spyOnImplementing(process.stdin, 'read', () => '');
process.stdin.read(1024);
expect(mockStdin).toHaveBeenCalledWith(1024);