feat: add getVariable function

[tonykogias]

Description
This commit introduces a new function for mock contracts. With getVariable you can view an internal variable's value.

Approach
A rough idea of how I approached this problem is:

1. I get an array of slot keys using getVariableStorageSlots that represent the position of the variable's value.
2. I get the values that are stored in those slots using the vmManager.getContractStorage function and providing the contract address and the appropriate slot key.
3. I decoded the values using the decodeVariable function and providing all the values from the above step which results in the variable's value

Metadata

• Fixes Add a way to view internal variables value #14

[wei3erHase]

yo @tonykogias, i'm very pleased to be reading this PR 😍
although the very precise commenting, got quite lost on the deep TS/EVM logic, but the tests seem to be working fine, so congrats for that gud ser 👏
made a few comments, will probably give a further review w/ @0xGorilla before approving 🚀
looks like it was way harder than it initially appeared, but you definitely have found the spot

oh this fell, i guess it's yours, KING
{\__/}
( • . •)
/ > 👑

[0xGorilla]

let's please add a warning, mentioning the things that don't work. Will links to PRs

[tonykogias]

done!

[0xGorilla]

Completely 🔥, well done

[ddnexus]

This is great and in regular contract deployment it works, however if I try to use it with an OZ UUPS proxy I get:

getVariable is not a function

The contract must be deployed using the upgrades.deployProxy() from the OZ upgrades HH plugin, and I managed to get no complaints from typescript:

const ProxyMock = await smock.mock("MyContract");
const proxyMock = await upgrades.deployProxy(ProxyMock as MockContractFactory<MyContract__factory> & MyContract__factory, [...]) as MyContract & MockContract<MyContract>;

However that does not seem to help. What did I miss?

Is there any possibility to pass a contract instance or a contract factory instead a contractName to smock.moch... Like what we can do with the smock.fake?

Currently I need to use a preprocessor to conditionally add a bunch of accessors to the contract just to handle the private variables for unit testing. The getVariable/setVariable would get rid of all that mess!

Is there any work around I could try?

Thanks