nedb/test_lac/loadAndCrash.test.js

/* eslint-env mocha */
/**
 * Load and modify part of fs to ensure writeFile will crash after writing 5000 bytes
 */
const fs = require('fs')
const { Writable } = require('stream')
const { callbackify } = require('util')

fs.promises.writeFile = async function (path, data) {
  let onePassDone = false
  const options = { encoding: 'utf8', mode: 0o666, flag: 'w' } // we don't care about the actual options passed

  const filehandle = await fs.promises.open(path, options.flag, options.mode)
  const buffer = (data instanceof Buffer) ? data : Buffer.from('' + data, options.encoding || 'utf8')
  let length = buffer.length
  let offset = 0

  try {
    while (length > 0) {
      if (onePassDone) { process.exit(1) } // Crash on purpose before rewrite done
      const { bytesWritten } = await filehandle.write(buffer, offset, Math.min(5000, length)) // Force write by chunks of 5000 bytes to ensure data will be incomplete on crash
      onePassDone = true
      offset += bytesWritten
      length -= bytesWritten
    }
  } finally {
    await filehandle.close()
  }
}

class FakeFsWriteStream extends Writable {
  constructor (filename) {
    super()
    this.filename = filename
    this._content = Buffer.alloc(0)
  }

  _write (chunk, encoding, callback) {
    this._content = Buffer.concat([this._content, Buffer.from(chunk, encoding)])
    callback()
  }

  _end (chunk, encoding, callback) {
    this._content = Buffer.concat([this._content, Buffer.from(chunk, encoding)])
    callback()
  }

  close (callback) {
    callbackify(fs.promises.writeFile)(this.filename, this._content, 'utf8', callback)
  }
}

fs.createWriteStream = path => new FakeFsWriteStream(path)

// End of fs monkey patching
const Nedb = require('../lib/datastore.js')
const db = new Nedb({ filename: 'workspace/lac.db' })

db.loadDatabaseAsync() // no need to await