feat(tests): add test "framework" for BN254 precompiles

[chfast]

🗒️ Description

Add test "framework" for BN254 precompiles: spec.py with some constants and conftest.py with generic fixtures.

🔗 Related Issues or PRs

#1860

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  uvx tox -e static

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[chfast]

I mostly copied the conftest.py from BLS precompiles tests. This works nicely here too because it uses features from Byzantium. So you may want to extract this as a tool for any other precompile testing. However, it will not work for eariler precompiles without modifications.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.26%. Comparing base (dca59f6) to head (590d4a9).
⚠️ Report is 2 commits behind head on forks/amsterdam.

Additional details and impacted files

@@                 Coverage Diff                 @@
##           forks/amsterdam    #1871      +/-   ##
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+ Coverage            86.15%   86.26%   +0.10%     
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  Files                  538      538              
  Lines                34557    34557              
  Branches              3222     3222              
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+ Hits                 29773    29809      +36     
+ Misses                4177     4161      -16     
+ Partials               607      587      -20     

Flag	Coverage Δ
unittests	86.26% <ø> (+0.10%)	⬆️

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[danceratopz]

Thanks @chfast, very nice!

Re-using the existing BLS pytest fixtures is a good idea. I think we should move these to a central place now in the scope of this PR.

I see two options:

1. Add them to a new module tests/common/precompile_fixtures.py and import them as required from there - this enables explicit local use of these fixtures and avoids defining them globally for all tests.
2. Add them to a new fill plugin that is loaded by default (via fill's pytest ini file) and globally scoped.

Although it's a new pattern, I prefer 1. to avoid polluting the test session with fixtures that intended to have a limited scope. Having these fixtures available globally increases the risk of error in unrelated tests that use fixtures that (accidentally) have the same names (the implementer could forget to shadow one or more of the fixtures, leading to unexpected behavior). We could consider using more ambiguous naming, but that's no absolute guarantee that they won't get used by mistake.

If you're happy with 1. Please add it to this PR and state briefly in the new module which type of precompiles could make use of it and why earlier precompiles can't use it. Thanks!

[danceratopz]

Thanks! One minor nit!

[danceratopz]

Could you please improve the docstring here?

state briefly in the new module which type of precompiles could make use of it and why earlier precompiles can't use it. Thanks!

[danceratopz]

Thanks!