如何使用 Jest 测试 Node.js 脚本的“if (require.main === module)”部分中的代码？

Question

I have written a function like this:

const myFunction = () => {
  return 'text';
};
exports.myFunction = myFunction;
if (require.main === module) {
  console.log(myFunction());
}

and this is my test:

const { myFunction } = require('../myFunction');

describe('test', () => {
  it('should return the text', () => {
    expect(myFunction()).toMatch('text');
  });
});

According to code coverage tools, every line in the code is covered except for this line line:

console.log(myFunction());

Based on comments, I think maybe the reality is that this line cannot be tested, so I'm updating my question:
How can I:

1. Test this line with Jest, understanding that it may not actually tick the "covered" box, but so I can literally test it. Because not every one of my files has such trivial code in that block. Sometimes I do want to test it for real.
2. Cause the coverage statistic to show the file as 100% covered? Not because I am pedantic, but I like using the coverage report to find things I need to add tests for, and having dozens of "false negatives" in my report makes that more difficult.

Answer 1

Based on a suggestion in the comments, I found that I can use a child_process exec call within the test to test the output from the command line like this:

const util = require('util');
const exec = util.promisify(require('child_process').exec);
const { myFunction } = require('../myFunction');

describe('test', () => {
  it('should return the text', () => {
    expect(myFunction()).toBe('text');
  });
  it('should return the text when called via command line too', async () => {
    const { stdout } = await exec('node myFunction', {
      encoding: 'utf8',
    });
    expect(stdout).toBe('text\n');
  });
});

Further comments pointed out that without exporting that section of code, Jest can never see it, and hence, never test it, meaning it will never show as "covered". Therefore, once I am satisfied that it is "tested well enough" I can exclude it form my report by adding /* istanbul ignore next */ before the offending line like this:

const myFunction = () => {
  return 'text';
};
exports.myFunction = myFunction;
if (require.main === module) {
  /* istanbul ignore next */
  console.log(myFunction());
}

Answer 2

As explained here , Node.js require wraps script contents with wrapper code specified in Module.wrapper and evaluates it with vm.runInThisContext . This can be implemented in a test. It can be something like:

let Module = require('module');

...

jest.resetModules();
jest.spyOn(console, 'log');

let myModPath = require.resolve('../myFunction');
let wrapper = Module.wrap(fs.readFileSync(myModPath));
let compiledWrapper = vm.runInThisContext(wrapper, {});
let mockModule = new Module(myModPath);
let mockExport = mockModule.exports;
let mockRequire = Module.createRequire(myModPath);
mockRequire.main = mockModule;
    
wrapper(mockExport, mockRequire, mockModule, path.basename(myModPath), path.dirname(myModPath));

expect(console.log).toBeCalledWith('test');