What does 'pending' test mean in Mocha, and how can I make it pass/fail?

I am running my tests and noticed:

18 passing (150ms)
1 pending

I haven't seen this before. Previously test either passed, or failed. Timeouts caused failures. I can see which test is failing because it's also blue. But it has a timeout on it. Here's a simplified version:

test(`Errors when bad thing happens`), function(){
  try {
    var actual = doThing(option)        
  } catch (err) {
    assert(err.message.includes('invalid'))
  }
  throw new Error(`Expected an error and didn't get one!`)
}

What does 'pending' mean? How could a test be 'pending' when Mocha has exited and node is no longer running?
Why is this test not timing out?
How can I make the test pass or fail?

Thanks!

Solution

The test had a callback (ie, an actual function, not done) but refactoring the code solved the issue. The issue was how code that expects error should run:

test('Errors when bad thing happens', function() {
  var gotExpectedError = false;
  try {
    var actual = doThing(option)       
  } catch (err) {
    if ( err.message.includes('Invalid') ) {
      gotExpectedError = true
    }
  }
  if ( ! gotExpectedError ) {   
    throw new Error(`Expected an error and didn't get one!`)
  }
});