Why can't I catch solidity errors testing with truffle?

Question

I'm testing the ERC20 standard. I try to send a transaction from an account with balance=0, which should throw an error. I'm trying to catch it.

In my test function, I'm using the following:

contract('erc20 deployed', function(accounts) {
    it("should not transfer 1 token from address[0] to address[1]", function(done) {
        try{
            return erc20Instance.transfer(accounts[1], 1);
            should.fail("No error was thrown trying to cheat balance");
        }
        catch(error){
            done();
        }
    });
});

When I execute it with truffle test I get the following error:

  1) Contract: erc20 deployed
       should not transfer 1 token from address[0] to address[1]:
     Uncaught Error: VM Exception while processing transaction: revert

How can I catch it? My goal is to test the the transfer function, testing that address[0] can not effectively make the transaction.

Answer 1

Try this:

contract('erc20 deployed', function(accounts) {
    const REVERT = "VM Exception while processing transaction: revert";
    it("should not transfer 1 token from address[0] to address[1]", async function() {
        try {
            await erc20Instance.transfer(accounts[1], 1);
            throw null;
        }
        catch (error) {
            assert(error, "Expected an error but did not get one");
            assert(error.message.startsWith(REVERT), "Expected '" + REVERT + "' but got '" + error.message + "' instead");
        }
    });
});

Answer 2

As an alternative to goodvibration's answer, it's also possible to use my truffle-assertions library, which includes a helper function to assert that a contract function reverts.

It can be installed through npm

npm install truffle-assertions

Next, it can be imported at the top of your test file

const truffleAssert = require('truffle-assertions');

Then it can be used inside your test:

contract('erc20 deployed', function(accounts) {
    it("should not transfer 1 token from address[0] to address[1]", async function() {
        await truffleAssert.reverts(erc20Instance.transfer(accounts[1], 1), null, "No error was thrown trying to cheat balance");
    });
});

The full documentation can be found on GitHub.