feat request: mocking Diamond proxy schemes

[hickscorp]

This is not a bug report - rather it's probably the start of a discuthis ssion, which could either lead to discovering that smock could have new features around the diamond pattern, or a contribution from people who found ways to do things neatly.

Consider the following architecture:

• You have a contact named Diamond.
• You have several facets - say FacetA and FacetB.
• You want to test FacetA, and you don't want to mix concerns from FacetB - in a nutshell, you would like to somehow act as if FacetB would be a separate contract.

At this point, I found myself stuck - because although FacetA and FacetB are split into different contacts, all their methods are in fact accessible through the Diamond contract. I didn't find a way to mock FacetB - and I found myself quite often testing things from the FacetA tests that are relevant to FacetB and reciproquelly.

I think since Diamonds often use libraries for functions that are reused across facets, there could be overlap with #50 ... But it's not always the case. Very often in FacetA.sol there are calls such as FacetB(address(this)).someFunction() - and it's not something that smock can help with unfortunatelly.

Can we maybe brainstorm a bit - it might be that I am missing something obvious here - but if not, I think it would be of great help to think about how smock could be improved to help with the diamond pattern.

One of the solution I found which would potentially work, would be to have some facets duplicated just for tests... But that would require quite some boilerplate written in solidity all the time - for example having FacetBMock.sol have a fallback() function which would record all calls so that they could be inspected by the typescript test - return values wouldn't work though.

Another option would be to allow smock to "connect" to an existing address... For example the flow would look like:

• Deploy diamond with only FacetA.
• Create a mock of FacetB (Eg smock.mock('FacetB')) and perform a diamondCut` to set it on the diamond.

In case it helps gathering ideas: this is a stack overflow post I've made regarding this particular topic.

[wei3erHase]

hi @hickscorp,
could you provide a basic example within the smock repo of a diamond deployment and the expected behaviour?
we're not very experienced with proxies and i'm afraid i do not totally understand how the feature would work.
if you can include the required packages and some test contracts, i can help you to develop the tests and add it as a bounty to develop

[hickscorp]

I will!

[hickscorp]

@wei3erHase happy to team up together today if you have a bit of time. We could get clean requirements written together?

[hickscorp]

I made a repository which has a README explaining the specs: https://github.com/hickscorp/smock-diamond-showcase