Test ethereum Event Logs with truffle - events

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

You are passing tx hash into done() function. I think the problem is in line:
insurance.send({from: accounts[0], value: web3.toWei(5, 'ether')}).then(done).catch(done);
Change it to:
insurance.send({from: accounts[0], value: web3.toWei(5, 'ether')}).then(function() { done(); }).catch(done);
To test for events:
it("should check events", function(done) {
var watcher = contract.Reward();
// we'll send rewards
contract.sendReward(1, 10000, {from: accounts[0]}).then(function() {
return watcher.get();
}).then(function(events) {
// now we'll check that the events are correct
assert.equal(events.length, 1);
assert.equal(events[0].args.beneficiary.valueOf(), 1);
assert.equal(events[0].args.value.valueOf(), 10000);
}).then(done).catch(done);
});

Answer 2

Since Truffle v3 you get the logs in the callback result. So you could do something like:
insurance.send({from: accounts[0], value: web3.toWei(5, 'ether')}).then((result) => {
assert.equal(result.logs[0].event, "Error", "Expected Error event")
})
See https://github.com/trufflesuite/truffle-contract#processing-transaction-results

Answer 3

There is a helper to do just this:
npm install --save truffle-test-utils
At the top of your test:
require('truffle-test-utils').init();
In your test:
let result = await insurance.send({from: accounts[0], value: web3.toWei(5, 'ether')});
assert.web3Event(result, {
event: 'Error',
args: {
error: 'Must send 10 ether'
}
}, 'Error event when sending 5 ether');
Full disclosure: I'm the author of this package. I wrote it after looking for such solution on SO, but couldn't find it.

Answer 4

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.

Answer 5

You can use the truffle-assertions package, which has an assertion to check that an event has been emitted. It also has the option to pass a filter function in order to check complex conditions to the event arguments.
npm install truffle-assertions
You can import it at the top of your test file:
const truffleAssert = require('truffle-assertions');
And use it inside your test:
let txResult = await insurance.send({from: accounts[0], value: web3.toWei(5, 'ether')});
truffleAssert.eventEmitted(txResult, 'Error', (ev) => {
return ev.error === 'Must send 10 ether';
}
Disclaimer: I created this package to use in my own tests, and by adding the filter function, it is possible to check complex conditions to the event arguments, in a very straightforward way. I wrote an article explaining this in more detail on my blog.

Answer 6

I was able to track down some references to help with this, especially if you want to use async/await.
it('can create a unique star and get its name', async function () {
const event = this.contract.starClaimed({});
event.watch(async (err, result) => {
if (err) console.log("Somethings wrong...");
if (result.args.owner === accounts[0]) {
let token = result.args._token;
event.stopWatching;
const star = await this.contract.tokenIdToStarInfo(token);
assert.equal(star[0], 'awesome star!');
assert.equal(star[1], 'yada yada yada');
assert.equal(star[2], 'dec_test');
assert.equal(star[3], 'mag_test');
assert.equal(star[4], 'cent_test');
}
});
await this.contract.createStar('awesome star!', 'yada yada yada', 'dec_test', 'mag_test', 'cent_test', {from: accounts[0]});
});
Here's the reference I found: https://github.com/trufflesuite/truffle-contract/issues/117