Using Jest to test a command line tool

Question

I have an app which exposes a script as a command. How do I test this script using jest. More specifically how to execute this script using jest and then apply the corresponding expectations? The script does not export any functions, It just contains a bunch of lines of code which are executed sequentially.

Answer 1

You could wrap your code in a main function, export it, and only run the function when executing the module from the command line, and then write tests for it. A simplified example could be:

// script.js
const toUpper = text => text.toUpperCase();
module.exports.toUpper = toUpper;

// It calls the function only if executed through the command line
if (require.main === module) {
  toUpper(process.argv[2]);
}

And then import the toUpper function from the test file

// script.test.js
const { toUpper } = require('./script');

test('tranforms params to uppercase', () => {
  expect(toUpper('hi')).toBe('HI');
});

See Node: Accessing the main module