npx hardhat test (error)

[solidcodes]

Hello guys, when I run a hardha ttest it shows these error messages below, how to fix?

An unexpected error occurred:

TypeError: Class extends value undefined is not a constructor or null
at Object. (C:\Users\solid\hardhat-tutorial\node_modules@nomicfoundation\hardhat-verify\src\internal\errors.ts:9:41)
at Module._compile (node:internal/modules/cjs/loader:1706:14)
at Object..js (node:internal/modules/cjs/loader:1839:10)
at Module.load (node:internal/modules/cjs/loader:1441:32)
at Function._load (node:internal/modules/cjs/loader:1263:12)
at TracingChannel.traceSync (node:diagnostics_channel:322:14)
at wrapModuleLoad (node:internal/modules/cjs/loader:237:24)
at Module.require (node:internal/modules/cjs/loader:1463:12)
at require (node:internal/modules/helpers:147:16)
at Object. (C:\Users\solid\hardhat-tutorial\node_modules@nomicfoundation\hardhat-verify\src\index.ts:27:1)

If you think this is a bug in Hardhat, please report it here: https://hardhat.org/report-bug

[kanej]

Hey @solidcodes, we would need some more details to help, are you able to push a minimal reproducible example: https://stackoverflow.com/help/minimal-reproducible-example ?

[sohailblockchain]

Hi! This error is typically caused by corrupted dependencies or version conflicts in your Hardhat project.

Solution 1: Clean Install (Most Common Fix) ✅

Try this first - it solves 90% of these errors:

# Delete node_modules and package-lock.json
rm -rf node_modules package-lock.json

# Clear npm cache
npm cache clean --force

# Reinstall dependencies
npm install

If you're on Windows (which I see you are), use:

rmdir /s /q node_modules
del package-lock.json
npm cache clean --force
npm install

Then try running your test again:

npx hardhat test

---

Solution 2: Check Node.js Version

Hardhat v3 requires Node.js 18 or higher.

Check your version:

node --version

If you're on Node.js 16 or lower, upgrade to Node.js 18 or 20 from: https://nodejs.org/

---

Solution 3: Update Hardhat and Plugins

Make sure all your packages are compatible:

npm install --save-dev hardhat@latest
npm install --save-dev @nomicfoundation/hardhat-toolbox@latest
npm install --save-dev @nomicfoundation/hardhat-verify@latest

Then reinstall:

rm -rf node_modules package-lock.json
npm install

---

Solution 4: Use Legacy Peer Dependencies

If the above doesn't work, try:

npm install --legacy-peer-deps

---

Check Your hardhat.config.js

Make sure you're importing the verify plugin correctly:

require("@nomicfoundation/hardhat-toolbox");
require("@nomicfoundation/hardhat-verify");

module.exports = {
  solidity: "0.8.28",
  // ... rest of your config
};

---

Most Likely Fix:

Based on your error, I'd recommend Solution 1 (clean reinstall) first. This usually resolves the "Class extends value undefined" error.

Let me know if this works! If you still get the error, share your package.json and I can help debug further. 👍

[sueun-dev]

This stack trace starts inside @nomicfoundation/hardhat-verify, so I would check version mix first.

npx hardhat test does not need the verify plugin at all.

First, print the versions you actually have:

npm ls hardhat @nomicfoundation/hardhat-verify @nomicfoundation/hardhat-ethers @nomicfoundation/hardhat-toolbox

Then do one quick check:

• remove the hardhat-verify import from your config for a minute
• run npx hardhat test again

If tests start working, the problem is the plugin version mix, not your test code.

Right now the current Hardhat 3 line is:

• hardhat@3.1.11
• @nomicfoundation/hardhat-verify@3.0.12
• @nomicfoundation/hardhat-ethers@4.0.6

If your project mixes Hardhat 3 with older plugin versions, this kind of error is expected.