Test for expected failure in Mocha

Question

Using Mocha, I am attempting to test whether a constructor throws an error. I haven\'t been able to do this using the expect syntax, so I\'d like to do the following:

<

Answer 1

MarkJ's accepted answer is the way to go and way simpler than others here. Let me show example in real world:

function fn(arg) {
  if (typeof arg !== 'string')
    throw TypeError('Must be an string')

  return { arg: arg }
}

describe('#fn', function () {
  it('empty arg throw error', function () {
    expect(function () {
      new fn()
    }).to.throw(TypeError)
  })

  it('non-string arg throw error', function () {
    expect(function () {
      new fn(2)
    }).to.throw(TypeError)
  })

  it('string arg return instance { arg:  }', function () {
    expect(new fn('str').arg).to.be.equal('str')
  })
})