iden3/circom_tester

Provides tools for testing circom circuits.

circom tester

Setup

1. Create new node js project.
2. Install circom_tester and chai packges.
3. Install mocha packge to run the tests.

Creating & Running a test file

Create a js file contain the following code or use the src provided in the following section.
Execue mocha -p -r ts-node/register 'multiplier2.js' to run the test file.

multiplier2.js (src)

const chai = require("chai");
const path = require("path");
const wasm_tester = require("./../index").wasm;
const c_tester = require("./../index").c;

const F1Field = require("ffjavascript").F1Field;
const Scalar = require("ffjavascript").Scalar;
exports.p = Scalar.fromString("21888242871839275222246405745257275088548364400416034343698204186575808495617");
const Fr = new F1Field(exports.p);

const assert = chai.assert;

describe("Simple test", function () {
    this.timeout(100000);

    it("Checking the compilation of a simple circuit generating wasm", async function () {
        const circuit = await wasm_tester(path.join(__dirname, "Multiplier2circom"));
        const w = await circuit.calculateWitness({a: 2, b: 4});
        await circuit.checkConstraints(w);
    });
});

circom_tester's Issues

Update vulnerable snarkjs

...So that NPM would not complain

tester.js doesn't check circom2

Before creating a PR wanted to make sure I'm getting this correctly.

When using circom-hardhat both circom and circom2 are installed.

In tester.js it checks the compiler version above 2.0 against circom and it returns false. For this use case we could implement:

let output = (await exec('circom2 --version')).stdout;

instead of:

let output = (await exec('circom --version')).stdout;

Should we check circom2 version, and then if it fails we check circom to cover both cases?

Inputs are assigned wrong values when there is a mistake in array-typed input size

Working with quite a complex circuits I figured out one weird behavior of WitnessCalculator which make my team spend a lot of time trying to figure out the root cause and fix it.

Preconditions:

1. Some circuit has an input of array type
2. There is at least one more input following the array type input in the circuit source code
3. The value which is assigned to array input has (by mistake) more elements than is expected

Expected behaviour by usual development practice:

The test framework should throw some exception that the input has wrong number of elements

Actual behaviour:

Nothing is thrown but the extra values in the array just ASSIGNED TO THE NEXT INPUT(S) !!!

Example:

template Example () {
    signal input a[2];
    signal input b;
    signal output c;
    log (a[0]);
    log (a[1]);
    log (b);

    a[1] === 0;
    c <== a[0] * b;
    c === 10;
}

component main = Example();

These inputs will work:

/* INPUT = {
    "a": ["5", "0"],
    "b": "2"
} */

These inputs will break c === 10; constraint as "b" will be "overlapped" with the third element of "a", which is 3

/* INPUT = {
    "a": ["5", "0", "3"],
    "b": "2"
} */

You can easily check the above in https://zkrepl.dev/

Suggestion: Mention 'circomkit'

'circomkit' is a really nice test & development environment for Circom. If you like it too maybe mention it in your README.

circom: command not found

circom was not found by the test-running instance; however, it is installed.

It happens on a fresh clone after following the setup procedures.

getDecoratedOutput and assertOut errors

I am trying to test my circom circuit but am getting errors.

Generating the witness using let witness = await circuit.calculateWitness({ a: inputA, b: inputB }); works as expected.

Then I am trying these two functions but I get errors:
await circuit.getDecoratedOutput(witness) gives ReferenceError: utils is not defined

and
await circuit.assertOut(witness, expectedOutput) gives AssertionError: Output variable not defined: main[0]

I have no idea what this means and how to fix it. Does someone have any idea?

r1csfile is extremely old

In daf3b0e the version of r1csfile was downgraded from the newer version to v0.0.16 which is now over a year and a half old. We've landed many improvements, bug fixes, and dependency updates in that time.

It's not clear why circom_tester needs to use such an old version of this dependency.