This code generates files that test if a value has the correct "typeof" value.

test-creator.js

const fs = require('fs');
const assert = require('assert');
const typeofResults = ['number', 'bigint', 'boolean', 'symbol', 'string', 'object'];

typeofResults.forEach(result => {
  fs.writeFileSync(`./is-${result}.js`, `module.exports = function (x) {
	  return typeof x === '${result}';
  }`);
});

// # Testing
function testType (typePredicate, type, correctValue, incorrectValue) {
	const moduleName = `is-${type}`;
	assert(typePredicate(correctValue), `✖ ${moduleName} failed when it should have passed`);
	assert(!typePredicate(incorrectValue), `✖ ${moduleName} passed when it should have failed`);
	console.log(`✔ ${moduleName} passed on value tests`);
}

// Now we need to test each file.
typeofResults.forEach(result => {
	const typePredicate = require(`./is-${result}.js`);

	switch (result) {
		case 'number':
			testType(typePredicate, 'number', 2, '');
			break;

		case 'bigint':
			testType(typePredicate, 'bigint', 11n, true);
			break;

		case 'boolean':
			testType(typePredicate, 'boolean', true, 2);
			break;

		case 'symbol':
			testType(typePredicate, 'symbol', Symbol('abc'), false);
			break;

		case 'string':
			testType(typePredicate, 'string', '', 2);
			break;

		case 'object':
			testType(typePredicate, 'object', {}, 2);
			break;

		// We should never hit this
		default:
			throw new Error('invalid type');
	}
});