jest-mock-process

Easily mock NodeJS process properties in Jest.

Installation

1npm install --save-dev jest-mock-process

Usage

TypeScript example.

1import {
2  mockProcessExit,
3  mockProcessStdout,
4  mockProcessStderr,
5  mockProcessUptime,
6  mockConsoleLog,
7} from "jest-mock-process";
8
9let mockExit = mockProcessExit();
10process.exit(1);
11expect(mockExit).toHaveBeenCalledWith(1);
12mockExit = mockProcessExit(new Error("Mock"));
13expect(() => process.exit(0)).toThrowError("Mock");
14
15const mockStdout = mockProcessStdout();
16process.stdout.write("Hello, world!");
17expect(mockStdout).toHaveBeenCalledWith("Hello, world!");
18
19const mockStderr = mockProcessStderr();
20process.stderr.write("Error");
21expect(mockStderr).toHaveBeenCalledWith("Error");
22
23const mockUptime = mockProcessUptime(3.14159);
24const uptimeValue = process.uptime();
25expect(uptimeValue).toEqual(3.14159);
26
27const mockLog = mockConsoleLog();
28console.log("Browser log");
29expect(mockLog).toHaveBeenCalledWith("Browser log");
30
31mockExit.mockRestore();
32mockStdout.mockRestore();
33mockStderr.mockRestore();
34mockUptime.mockRestore();
35mockLog.mockRestore();

Advanced usage

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

1import { mockedRun, MockedRunResult } from "jest-mock-process";
2
3const mockRun = mockedRun({
4  stdout: mockProcessStdout,
5  stderr: mockProcessStderr,
6  exit: mockProcessExit,
7  log: mockConsoleLog,
8});
9const mockEnvironment = mockRun(() => {
10  process.stdout.write("stdout payload");
11  process.stderr.write("stderr payload");
12  process.exit(-1);
13  console.log("log payload");
14  return 10;
15});
16expect(mockEnvironment.result).toEqual(10);
17expect(mockEnvironment.error).toBeUndefined();
18expect(mockEnvironment.mocks.stdout).toHaveBeenCalledTimes(1);
19expect(mockEnvironment.mocks.log).toHaveBeenCalledWith("log payload");

NOTE: The above is a breaking change in version 2.0.0, as the provided mocks are now limited to the mocks object.

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

1import { spyOnImplementing } from "jest-mock-process";
2
3const mockStdin = spyOnImplementing(process.stdin, "read", () => "");
4process.stdin.read(1024);
5expect(mockStdin).toHaveBeenCalledWith(1024);