Test ethereum Event Logs with truffle

Question

I have a contract's function which emit events on each call.

I would like to have an event emitted on each test which are passing, here are some tests :

it("should emit Error event when sending 5 ether", function(done){
  var insurance = CarInsurance.deployed();

  insurance.send({from: accounts[0], value: web3.toWei(5, 'ether')}).then(done).catch(done);
});

it("should emit Error event when sending 5 ether", function(done){
  var insurance = CarInsurance.deployed();

  insurance.send({from: accounts[0], value: web3.toWei(5, 'ether')}).then(function(txHash){
    assert.notEqual(txHash, null);
  }).then(done).catch(done);
});

it("should emit Error event when sending 5 ether", function(done){
  var insurance = CarInsurance.deployed();

  insurance.send({from: accounts[0], value: web3.toWei(5, 'ether')}).then(function(done){
    done();
  }).catch(done);
});

The results are :

1) should emit Error event when sending 5 ether

Events emitted during test:
---------------------------

Error(error: Must send 10 ether)

---------------------------
✓ should emit Error event when sending 5 ether (11120ms)
✓ should emit Error event when sending 5 ether (16077ms)


3 passing (51s)
1 failing

1) Contract: CarInsurance should emit Error event when sending 5 ether:
 Error: done() invoked with non-Error: 0x87ae32b8d9f8f09dbb5d7b36267370f19d2bda90d3cf7608629cd5ec17658e9b

You can see that the only one which is logged fail.

Any idea ?

Thank you

Answer 1

Instead of writing your own, you can also use Truffle's test utils expectEvent.js:

const { inLogs } = require('openzeppelin-solidity/test/helpers/expectEvent')
require('chai').use(require('chai-bignumber')(BigNumber)).should()
...
{ logs: this.logs } = await this.token.burn(amount, { from: owner })
...
const event = inLogs(this.logs, 'Burn')
event.args.burner.should.eq(owner)
event.args.value.should.be.bignumber.equal(amount)

An example can be found in Truffle's BurnableToken.behavior.js.