The return value of GrandSumVerifier should be tested.

[qpzm]

Description

GrandSumVerifier.verifyProof is not a view function.
https://github.com/summa-dev/summa-solvency/blob/fec83a747ead213261aecfaf4a01b43fff9731ee/contracts/src/GrandSumVerifier.sol#L32

This is a generated type in contracts/typechain-types/src/GrandSumVerifier.ts when running tests.

verifyProof(
  vk: PromiseOrValue<string>,
  proof: PromiseOrValue<BytesLike>,
  values: PromiseOrValue<BigNumberish>[],
  overrides?: Overrides & { from?: PromiseOrValue<string> }
): Promise<ContractTransaction>;

It does not return the bool value that GrandSumVerifier.verifyProof returns so the test just checks whether the function is not reverted. However, the function does not revert when I change the input total_balances.
https://github.com/summa-dev/summa-solvency/blob/fec83a747ead213261aecfaf4a01b43fff9731ee/contracts/test/Verifiers.ts#L96

POC

Change total_balances to random values and then run npx hardhat test.
https://github.com/summa-dev/summa-solvency/blob/fec83a747ead213261aecfaf4a01b43fff9731ee/prover/bin/commitment_solidity_calldata.json#L5-L6

{
  "range_check_snark_proof": "...",
  "grand_sums_batch_proof": "...",
  "total_balances": [
    "0x1087f3e0000000000000",
    "0x197f3000000000000000"
  ]
}

In Verifier.ts, GrandSum Proof Verifier > should verify grand sum proof test passes.
https://github.com/summa-dev/summa-solvency/blob/fec83a747ead213261aecfaf4a01b43fff9731ee/contracts/test/Verifiers.ts#L96

Fix

1. add view modifier to GrandSumVerifier.verifyProof

-    ) public returns (bool) {
+    ) public view returns (bool) {

https://github.com/summa-dev/summa-solvency/blob/fec83a747ead213261aecfaf4a01b43fff9731ee/contracts/src/GrandSumVerifier.sol#L32

2. Test the return value.

-       expect(await grandSumVerifier.verifyProof(verifyingKey.address, proofs, totalBalances)).to.be.not.reverted;
+       expect(await grandSumVerifier.verifyProof(verifyingKey.address, proofs, totalBalances)).to.be.true;

https://github.com/summa-dev/summa-solvency/blob/fec83a747ead213261aecfaf4a01b43fff9731ee/contracts/test/Verifiers.ts#L96

3. check success and revert before pairing as in InclusionVerifier.sol.

    success := ec_add_tmp(success, lhs_x, lhs_y)
+   if iszero(success) {
+       revert(0, 0)
+   }

https://github.com/summa-dev/summa-solvency/blob/fec83a747ead213261aecfaf4a01b43fff9731ee/contracts/src/GrandSumVerifier.sol#L143-L144