truffle-test-utils

Helpers to support Truffle's JavaScript tests for Ethereum smart contracts

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truffle-test-utils
Utils to support Truffle's JavaScript tests for Ethereum smart contracts.

Install

npm install truffle-test-utils

How to use

To use these helpers, include them at the top of your tests:
require('truffle-test-utils').init();

Utils

Event testing

Single event

To make sure a smart contract call generates the expected event:
// Regular call thanks to Truffle
let result = await testedSmartContract.testedFunction();
// Check event
assert.web3Event(result, {
  event: 'TestedEvent',
  args: {
    param_1: 'Some value',
    param_2: 0x123456 // No need for toNumber hassle
  }
}, 'The event is emitted');
By omitting the args parameter, only the event itself is tested, no matter what its arguments are:
let result = await testedSmartContract.testedFunction();
assert.web3Event(result, {
  event: 'TestedEvent'
  // Any argument is allowed
}, 'The event is emitted');
So to make sure that an event has no arguments, pass an empty hash:
let result = await testedSmartContract.testedFunction();
assert.web3Event(result, {
  event: 'TestedEvent',
  args: {} // Event should have no argument at all
}, 'The event is emitted');
Note that assert.web3Event makes sure that a particular event is emitted. If other events are emitted too, they are simply ignored.

Mutliple events

You can check several events at once with assert.web3SomeEvents and assert.web3AllEvents.
assert.web3SomeEvents checks the expected events and ignore additional events:
let result = await testedSmartContract.testedFunction();
assert.web3Events(result, [
  { event: 'E1' }, // testedFunction must emit E1
  { event: 'E2' }  // testedFunction must emit E2
   // What if testedFunction emits E3 too? It's okay
]);
assert.web3AllEvents checks that the expected events are emitted and no others:
let result = await testedSmartContract.testedFunction();
assert.web3AllEvents(result, [
  { event: 'E1' }, // testedFunction must emit E1
  { event: 'E2' }  // testedFunction must emit E2
   // What if testedFunction emits E3 too? The test fails
]);
assert.web3Events is an alias to assert.web3AllEvents.

expect

If you prefer expect, you can use it in place of assert:
// Regular call thanks to Truffle
let result = await testedSmartContract.testedFunction();
// Check event
expect.web3Event(result, {
  event: 'TestedEvent',
  args: {
    param_1: 'Some value',
    param_2: 0x123456 // No need for toNumber hassle
  }
}, 'The event is emitted');