Truffle return value from transaction method [duplicate]

Question

I am following this tutorial to make immutable token metadata for ERC1155 tokens.

https://coinsbench.com/fully-decentralized-erc-721-and-erc-1155-nfts-6c229adf9c9b

ERC1155 contract is here...

https://github.com/Aurelien-Pelissier/Medium/blob/main/Fully%20Decentralized%20ERC-721%20and%20ERC-1155%20NFTs/contracts/ERC1155.sol

When creating a Truffle test i am experiencing issues with this method in the above contract.

function mintToken(string memory tokenURI) public returns (uint256){
    //Do stuff
    return tokenId;
}

If i call the function in Truffle as 'normal', i get the transaction reciept and balance is correct. (TEST 1 - PASSES)

If i use the call method then i get the tokenId back, but if i check the balance of the account i get 0. (TEST 2 - FAILS)

const ERC = artifacts.require("MyNFT_ERC1155");

contract("ERC1155", (accounts) => {
  beforeEach(async () => {
    erc = await ERC.new();
  });
  describe("Mint", async () => {
    it("Mint and return the reciept", async () => {
      let tx = await erc.mintToken("https://web-site.com/something.json", "10");
      console.log("Transaction reciept");
      console.log(tx);
      //First token minted has known id of 0. This is not known in prod.
      const balance = await erc.balanceOf(accounts[0], 0);
      assert.equal(parseInt(balance), 10);
    });
    it("Mint and return the token id", async () => {
      let tokenId = await erc.mintToken.call(
        "https://web-site.com/something.json",
        "10"
      );
      console.log("Token Id");
      console.log(tokenId);
      const balance = await erc.balanceOf(accounts[0], tokenId);
      assert.equal(parseInt(balance), 10);
    });
  });
});

It seems like i need to use 'call' to get the tokenId, but how do i wait for the transaction to complete so that the balance is updated?

If i use this contract in other tests, how do i get the tokenId AND make sure the token was minted.

Regards

Answer 1

.call() is used only for functions that do not change the internal state of the smart contract i.e. do not modify the global variables.

In your case, you should make a new view function in solidity in order to use call

function get_last_tokenID() public view returns (uint256) {
    return(_tokenIds.current());
}

You can check more details about the .call() method here https://blockheroes.dev/when-to-use-call-solidity-functions-truffle/