Truffle test scripts - Help Please

Question

I want to know if my syntax is correct not how to catch a revert.

the task is: Call bid method from accounts[1] of Auction.sol using auctionInstance and pass itemId=0, count=6 as arguments

 it("Should NOT allow to bid more than remaining tokens", function() {
return auctionInstance.bid(itemId[0],count[6],{from:account[1]})
.then(function (result) {
  /*
  We are testing for a negative condition and hence this particular block will not have executed if our test case was correct. If this part is executed then we throw an error and catch the error to assert false
  */
  revert("Failed to check remaining tokens less than count");
}).catch(function (e) {
  var a = e.toString();
  if(e === "Failed to check remaining tokens less than count") {
  assert(false);
  } else {
    assert(true);
  }
})

The project code looks like this I had to complete it that is the code at the top.

   //Test Case for checking if the bid is more than the token amount
  it("Should NOT allow to bid more than remaining tokens", function() {
    /**********
    TASK 1:   Call bid method from accounts[1] of Auction.sol using auctionInstance and
    pass itemId=0, count=6 as arguments
    HINT:     To make a function call from account 1 use {from: accounts[1]} as an extra argument
    ***********/
    return //
    .then(function (result) {
      /*
      We are testing for a negative condition and hence this particular block will not have executed if our test case was correct. If this part is executed then we throw an error and catch the error to assert false
      */
      throw("Failed to check remaining tokens less than count");
    }).catch(function (e) {
      var a = e.toString();
      if(e === "Failed to check remaining tokens less than count") {
        /**********
        TASK 2: This is the error which we had thrown. Should you assert true or false?
        HINT:   Use assert(false) to assert false
                Use assert(true) to assert true
        ***********/
        //
      } else {
        /**********
        TASK 3: assert the opposite here
        ***********/
        //
      }
    })
  });

Answer 1

The most straightforward way to test for reverts is using my truffle-assertions library. It has options to assert that a transaction fails/reverts/passes.

You can install the library with npm

npm install truffle-assertions

Then import it at the top of your file

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

Then you can use it in your tests. In your case you could change your test to the following:

it("Should NOT allow to bid more than remaining tokens", function() {
    return truffleAssert.reverts(
        auctionInstance.bid(itemId[0], count[6], {from: account[1]}), 
        "Failed to check remaining tokens less than count"
    );
})

Or with async/await:

it("Should NOT allow to bid more than remaining tokens", async function() {
    await truffleAssert.reverts(
        auctionInstance.bid(itemId[0], count[6], {from: account[1]}), 
        "Failed to check remaining tokens less than count"
    );
})

Do note that right now you can only retrieve the revert reason string ("Failed to...") when using the latest versions of Truffle and ganache-cli. If you are using other versions, you should omit this parameter.