Calling event.watch() and event.get() prevents truffle JS tests to terminate

Question

My contract is

contract SimpleContract {
    uint storedData;
    event SimpleEvent(uint p); // EVENT

    function set(uint x) public 
    { 
      storedData = x; 
      SimpleEvent(x); // TRIGGER EVENT
    }
    function get() public returns (uint) { return storedData; }
}

When I execute this test with truffle test, the console listens forever and the test never ends.

var SimpleContract = artifacts.require("SimpleContract");

contract('SimpleContract', function(accounts) {
  let contract;
  let owner;
  let web3Contract;

  before(async () => {
    contract = await SimpleContract.deployed();
    web3Contract = web3.eth.contract(contract.abi).at(contract.address);
    owner = web3Contract._eth.coinbase;    
  });

  it("test", async function() {    
    let event = contract.SimpleEvent({_from: owner}, {fromBlock: 0, toBlock: 'latest'});

    // THIS TRIGGERS THE EVENT    
    await contract.set.sendTransaction(10);

    // PRINT THE PAST EVENT, BUT DOESN'T STOP THE EXECUTION
    event.get((error, logs) => {
      console.log(logs)      
    })    
  });  
});

If I keep executing the test (using truffle develop and then test multiple times), I get this message after 11 executions:

(node:382) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 unhandledRejection listeners added. Use emitter.setMaxListeners() to increase limit

Same behaviour with watch(), but in that case I can fix with:

event.watch(function(error, result) {
  if (error) {
    console.log(error)        
  } else {
    console.log(result)
  }
  event.stopWatching() // WITHOUT THIS, EXECUTION NEVER ENDS
})

There is some memory leak, I'm not releasing/unregistering correctly. Any idea?

Answer 1

This library might help keep the test script concise.

https://github.com/rkalis/truffle-assertions

If can look like this:

truffleAssert.eventEmitted(result, 'TestEvent');

or this, if you want to inspect event data:

truffleAssert.eventEmitted(result, 'TestEvent', (ev) => {
    return ev.param1 === 10 && ev.param2 === ev.param3;
});

or even like this is you want to confirm that a "bad news" event was not emitted:

truffleAssert.eventNotEmitted(result, 'TestEvent');

Hope it helps.