Chai test not creating database entry

My chai test creates the database entry but doesn’t add the ‘board’ value.
Is there some way to deal with a field that’s reference?

My mongoose object looks like:

const ThreadSchema = new Schema({
  "text": {
    'type': String
  },
  "delete_password": {
    'type': String,
    'select': false
  },
  "created_on": {
    'type': Date,
    'default': new Date()
  },
  "bumped_on": {
    'type': Date,
    'default': new Date()
  },
  "reported": {
    'type': Boolean,
    'select': false,
    'default': false
  },
  "replycount":{
    'type': Number,
    'default': 0
  },
  "board" : {
    'type': mongoose.Schema.Types.ObjectId,
    'ref': 'Board'
  },
  replies: [{
      'type': mongoose.Schema.Types.ObjectId,
      'ref': 'Reply'
    }]
});

and my test looks like

     test('All fields complete', function(done) {
       chai.request(server)
        .post('/api/threads/test')
        .send({
          text: 'test thread text',
          delete_password: 'password',
          board: ObjectId('5d8f748a1d788a3be2b9a7b7')
        })
        .end(function(err, res){
           expect(err).to.be.null;
           assert.equal(res.status, 200);
           expect(res.body).to.eventually.be.a('object');
          //assert.property(res.body.thread, 'text');
          done();
        });
      });