Mocha/Nightmare test failing but still waiting for timeout

Question

I'm running this test (simplified), which fails as expected ... but despite the failure, it still waits for the full 20 second timeout. How can I make it fail immediately?

it("should fail before timeout", function (done) {
      var nightmare = new Nightmare({ show: true })
        .goto(url)
        .evaluate(function () {
        })
        .then(function (result) {
          // this point is reached, and then the test just waits 
          // 20 seconds before finally failing
          throw "Fail" 
        })
    })

Answer 1

This is an error using mocha. Instead of throwing, then should call done with an Error object. (also replaced throw "Fail" with throw new Error("Fail"))