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JavaScript JavaScript Unit Testing Improving Our Tests Catching an Error

Yet another chai docs question (throwing an error)

So I thought this would be the right way to throw an error based on the video and previous examples. I really don't understand what I'm doing wrong here...

var expect = require('chai').expect

describe('subtraction', function () {
  var subtraction = require('./subtraction.js').subtraction;  
  it('only works with numbers', function () {
    var handler = function () {subtraction("a", "b");};
    expect(handler).to.throw('subtraction only works with numbers!');
function subtraction (number1, number2) {
  if (typeof number1 !== 'number' || typeof number2 !== 'number') {
    throw Error('subtraction only works with numbers!')
  return number1 - number2

module.exports.subtraction = subtraction;