const User = this.sequelize.define('user', {
  age: Sequelize.BIGINT
});

const age = BigInt(Number.MAX_SAFE_INTEGER).add(Number.MAX_SAFE_INTEGER);

return User.sync({force: true}).then(() => {
  return User.create({age});
}).then(user => {
  expect(BigInt(user.age).toString()).to.equal(age.toString());
  return User.findAll({
    where: {age}
  });
}).then(users => {
  expect(users).to.have.lengthOf(1);
  expect(BigInt(users[0].age).toString()).to.equal(age.toString());
});