function invokeMocha(args, done, opts = {}) {
  if (typeof args === 'function') {
    opts = done;
    done = args;
    args = [];
  }
  return createSubprocess(
    defaultArgs([MOCHA_EXECUTABLE].concat(args)),
    done,
    opts
  );
}
Invoke `mocha` with default arguments. Calls `done` upon exit. Does _not_ accept a fixture path.

Good for testing error conditions. This is low-level, and you likely want
{@link runMocha} or even {@link runMochaJSON} if you are running test fixtures.

@param {string[]|RawResultCallback} args - Args to `mocha` or callback
@param {RawResultCallback|Object} done - Callback or options
@param {Object} [opts] - Options
@returns {ChildProcess}