test: hexEqual accepts SkipCompare in TypeScript but rejects it at runtime

[Kewe63]

Summary

The TypeScript declaration for the custom hexEqual Chai matcher accepts SkipCompare, but the registered runtime implementation rejects the same value as invalid hexadecimal input.

This creates a deterministic mismatch between the test-helper contract and its runtime behavior.

Tested against commit: 3f1efe99bf129b16c276ae5b44b7a35247ffe5c5

Environment: Node.js v22.22.2, clean checkout, npm ci

Reproduction

Create tests/helpers/matchers/skipCompare.repro.test.ts:

/// <reference path="./types.d.ts" />
import { expect } from 'chai'
import './plugin'
import { skipCompare } from './skippable'

describe('hexEqual SkipCompare contract', () => {
  it('accepts SkipCompare as declared by the TypeScript signature', () => {
    expect(() => expect('0x12').to.hexEqual(skipCompare)).not.to.throw()
  })
})

Run:

node node_modules/mocha/bin/mocha.js \
  --require ts-node/register/transpile-only \
  tests/helpers/matchers/skipCompare.repro.test.ts

Observed result:

0 passing
1 failing

AssertionError: expected [Function] to not throw an error but
'AssertionError: Expected "0x12" to be a hex string equal to
"[object Object]", but "[object Object]" is not a valid hex string'
was thrown

An isolated TypeScript check accepts the call without errors. As a control, the standard skippable comparison succeeds at runtime:

expect('0x12').to.eq(skipCompare)

Expected behavior

Either:

• hexEqual(skipCompare) skips the comparison as declared; or
• SkipCompare is removed from the TypeScript signature if the behavior is intentionally unsupported.

Actual behavior

tests/helpers/matchers/types.d.ts accepts SkipCompare, but supportHexEqual() passes it to isHex(). Because the marker is an object, the matcher throws before comparison.

Root cause

The declaration includes the marker:

hexEqual(other: `0x${string}` | SkipCompare, message?: string): void

The runtime implementation validates both operands as hex strings without first checking isSkipCompare(other).

The generic supportSkippable() plugin only overwrites built-in comparison methods and does not wrap the custom hexEqual method.

Impact

This is a test-helper correctness defect, not a production or security vulnerability.

Callers following the TypeScript contract can write valid, compiling tests that fail deterministically at runtime. This makes partial expected-value structures using skipCompare unreliable when passed to hexEqual.

Suggested fix

If skip semantics are intended, handle SkipCompare before hexadecimal validation and add a regression test for:

expect('0x12').to.hexEqual(skipCompare)

Otherwise, remove SkipCompare from the declared hexEqual parameter type.

Duplicate check

I searched open and closed issues and pull requests using the affected symbol, marker type, file paths, error text, and behavior. I also inspected pull-request refs that touched the matcher files. No matching report or implementation was found.

#369 concerns the separate problem that the Hardhat unit-test suite is not executed by CI; it does not cover this runtime contract mismatch.