create-empty-file-of-size.js

const fs = require('fs');
const Promise = require('bluebird');

const createEmptyFileOfSize = (fileName, size) => {
  return new Promise((resolve, reject) => {
    try {
      fd = fs.openSync(fileName, 'w');
      fs.writeSync(fd, Buffer.alloc(1), 0, 1, Math.max(0, size-1));
      fs.closeSync(fd);
      resolve(true);
    } catch (error) {
      reject(error);
    }
  });
};

Since you create a Promise, the executor function passed to the Promise constructor should end as soon as possible (it is called by the Promise constructor).
The Promise constructor should complete immediately, leaving the Promise in the pending state. The Promise will complete its assignment asynchronously and change its status by calling the provided resolve or reject callbacks.

Use setTimeout(..., 0) to postpone the execution of the try/catch block after the completion of the current JavaScript event loop.

const fs = require('fs');
const Promise = require('bluebird');

const createEmptyFileOfSize = (fileName, size) => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
        try {
          fd = fs.openSync(fileName, 'w');
          fs.writeSync(fd, Buffer.alloc(1), 0, 1, Math.max(0, size-1));
          fs.closeSync(fd);
          resolve(true);
        } catch (error) {
          reject(error);
        }
    }, 0)
  });
};