Difference between contract.new and contract.deployed functions

Question

I have create a basic truffle project and i am writing automated tests.

There is 2 ways to instantiate the smartcontract to test and i want to understand the difference between this 2 ways:

const SimpleStorage = artifacts.require("./SimpleStorage.sol");
contract("SimpleStorage", accounts => {
  
  beforeEach( async () => {
     // Way 1:
     this.instance = await SimpleStorage.new({ from: accounts[0] });

     // Way 2:
     this.instance = await SimpleStorage.deployed();
  });

It works in both cases but i want to understand the differences between new and deployed

Thanks

Answer 1

.new() instructs it to deploy an instance of the contract.

.deployed() returns the deployed contract on the active network, with a twist. You can use that in a UI or nodejs app that wants the deployed contract, but truffle test uses a sandbox that is meant to prevent tests from scribbling on production contracts. So, test goes ahead and deploys a new one, just like new(), and it pretends that was the deployed contract.

Personally, my habit is to use new() so I know it is a new instance without reliance on the sleight-of-hand always working as expected. That method strikes me as more explicit and less vulnerable to future breaking changes or bugs in Truffle itself.

There is a good reason for the behavior. Developers might form the habit of using deployed() everywhere. In tests, it could lead to trouble, so the sandbox idea keeps them out of trouble. I treat this interception like an emergency circuit-breaker that shouldn't be the primary means or sole means of preventing a disaster, so new(), because that's what I actually want.

In practice, both work and the result is mostly the same. Maybe a kind soul will chime in with subtle differences if any exist.

Hope it helps.