test.js

/* eslint-env mocha */

const assert = require('assert');
const { AssertionError } = require('assert');

const { functionundertest } = require('../index');

describe('Testing Error States', () => {
  it('Throws an error when called with missing arguments', () => {
    try {
      functionundertest(); // this should fail
      assert.fail('expected exception not thrown'); // this throws an AssertionError
    } catch (e) { // this catches all errors, those thrown by the function under test
                  // and those thrown by assert.fail
      if (e instanceof AssertionError) {
        // bubble up the assertion error
        throw e;
      }
      assert.equal(e.message, 'Invalid Arguments');
    }
  });
});