Docs: Add SMT test spec and test fixtures

[bvrooman]

Related issues:

• Progress on Move SMT test fixtures to the fuel-specs repo  fuel-merkle#80

This PR adds the SMT test specification and related test fixtures currently living in the fuel-merkle repo to the fuel-specs repo. The fuel-specs repo is the appropriate housing for these documents since they describe universally applicable test outputs and are agnostic to any implementation. Sparse Merkle tree implementations can adhere to the SMT test specifications in fuel-specs to ensure correctness; this includes the fuel-merkle crate and fuel-merkle-sol library.

SMT libraries can include the fuel-specs repo as a git submodule in order to pull in the test fixtures.

In a future PR, I will remove the existing test spec and fixture files from fuel-merkle and specify fuel-specs as a submodule.

[Voxelot]

would it be more accurate to call these test_vectors instead of fixtures? Fixtures are typically just the environment / setup ingredients for a test rather than the actual SUT and expectations.

[bvrooman]

Yea, I agree, I think that's a good distinction. I've updated the folder name to test_vectors.

[Voxelot]

Git submodules can be a little tricky to manage sometimes.. Is there a way we could use git hooks to automatically pull these test-vectors into fuel-merkle?

[bvrooman]

I agree that submodules can be tricky: codebases that uses submodules have to remember to run all the submodule commands, i.e. git submodule init, git submodule update, etc, and clients have to stay on top of updates to the source repo manually.

I can look into alternative solutions, like git hooks. If we can automate pulling in the test vectors, that would be great.

That said, can we get the test vectors into fuel-specs in the meantime? I believe that this step will still need to come first regardless of whichever solution we go with.

[adlerjohn]

Verification is easier than execution after all, so my preference would instead be a CI workflow in fuel-merkle that pulls the test vectors from the latest master of fuel-specs and compares for diffs.

[adlerjohn]

utACK