2_deploy_contracts.js

const Storage = artifacts.require("./Storage.sol");

module.exports = function(deployer) {
  deployer.deploy(Storage);
};

Storage.sol

pragma solidity ^0.4.15;

contract Storage {
  mapping (uint => uint) public users;

  event SetUserData(uint userId, uint data);

  function setUserData(uint userId, uint data) public {
    require(users[userId] == 0);
    users[userId] = data;
    SetUserData(userId, data);
  }

  function getUserData(uint userId) constant public returns (uint data) {
    if (users[userId] != 0) {
      return users[userId];
    } else {
      return data;
    }
  }
}

StorageTest.js

const Storage = artifacts.require("./Storage.sol");

contract('Storage', function(accounts) {
  let storage;
  before(async () => {
    storage = await Storage.deployed();
  });
  it("Set user data", async () => {
    await storage.setUserData(1, 1234);
    const data = await storage.getUserData.call(1);
    assert.equal(data, 1234, 'Return user data');
  });
});