EVM runtime: implement unit tests for precompiles

[raulk]

Unit tests for #695, as per #695 (comment).

[raulk]

The sha256 precompile earned a unit test here: filecoin-project/builtin-actors#615.
But all other precompiles remain untested.

@maciejwitowski -- what do you think about closing this issue and opening one per precompile that requires a unit test, to track more granularly?

[maciejwitowski]

If we think testing all precompiles is big enough that we won't fit all in 1 week, then splitting them is a good idea.
@mriise could you help me and open 1 issue per each precompile which needs testing and add it to the Obsidian release https://github.com/filecoin-project/ref-fvm/milestone/11 ? (I wouldn't like to increase the scope of Iron now after we planned the week).

[mriise]

How extensive do we expect precompile tests to be? I dont think having an issue -per precompile test is needed, rather just a checklist.

• sha256
• ec_recover EVM: Fix Precompile Failure Modes & Implement Remaining Precompile Tests builtin-actors#654
• ripemd160 Add ripemd160 precompile test builtin-actors#651
• identity (this is just Vec::from(input), no need for a precompile)
• modexp EVM: Fix Precompile Failure Modes & Implement Remaining Precompile Tests builtin-actors#654
• ec_add
• ec_mul
• ec_pairing EVM: Fix Precompile Failure Modes & Implement Remaining Precompile Tests builtin-actors#654
• blake2f

[maciejwitowski]

@mriise thanks! Can we just move the unchecked ones to the new issue or more issues if we know these tests will take more than eg 2-3 days and may not fit all into a single release? The goal is never to have a single issue span multiple releases. Eg this one is assigned to Copper, so we can create a new one and assign it to one of the next releases.

[mriise]

This should all be finished in a few hours.

[maciejwitowski]

Closing this one as it will be addressed in #879