Add satisfy method to Chai emit matcher

[fracek]

I'm testing parts my smart contracts using fast-check (a property based testing library similar to quickcheck). In this case I'm interested in checking general properties of my system rather than specific values.

I propose to add an implementation of Chai's satisfy/satisfies to EmitAssertion that checks whether a predicate on the event is satisfied or not.

I can work on the issue and send a PR, I just wanted to hear your feedback before implementing it.

Example

await expect(token.transfer(walletTo.address, 7))
  .to.emit(token, 'Transfer')
  .satifies((_from, to, value) => to === walletTo && value === 7)

Related issues

• #437 Check against subset of args emitted in events
• #361 Matching any argument in a mock using withArgs()