Test refactoring for new-arc

[drahrealm]

Related Issues

• Test refactoring #21

Changes

• Based off the new-arc branch:
  • Added additional test scenarios
  • Added solidity-coverage package to help identifying possible missing (and important) test scenarios
  • Added helper method to streamline event args and signature assertions (via validateEvent) and apply it to all existing event tests
  • Change majority of immutable state variables to constant instead (ie. they already are assigned on declaration)
  • Remove redundant/duplicate calls to all constant state variables in tests
  • Split PirexCvx unit tests into 3 smaller groups based on action flow (base, main, reward)
  • Use folder-wide before hook to setup required variables commonly used for all tests

Notes

• Run npm i for the first time testing the PR due to new packages

[kphed]

I changed the other non-32 byte variables to constants, but for FEE_DISTRIBUTOR_ROLE, we should keep it as an immutable variable even if we don't set it in the constructor:

For a constant variable, the expression assigned to it is copied to all the places where it is accessed and also re-evaluated each time. This allows for local optimizations. Immutable variables are evaluated once at construction time and their value is copied to all the places in the code where they are accessed. For these values, 32 bytes are reserved, even if they would fit in fewer bytes. Due to this, constant values can sometimes be cheaper than immutable values.

ethereum/solidity#4024

It seems that constants may be more efficient in cases where the variable does not need 32 bytes allocated (would not be the case here).

Also, since constants are re-evaluated every time, wouldn't that increase runtime costs?

[drahrealm]

Both constant and immutable vars are replaced by their values at execution, so usual expensive gas cost from reading state vars won't apply here. Did some test run with gas reporter and I can confirm that immutable does cost a bit less gas than constant for bytes32, but more a bit more expensive for those smaller than bytes32 size. Good find 👍