fhevm-testing

FHEVM Hardhat Testing Rules

Setup

import { fhevm } from "hardhat";
import { FhevmType } from "@fhevm/hardhat-plugin";

Test Modes

Mode	Command	Encryption	Speed
Mock	npx hardhat test	Simulated	Fast
Local node	npx hardhat test --network localhost	Simulated	Fast
Sepolia	npx hardhat test --network sepolia	Real FHE	Slow

Encrypting Values

const input = fhevm.createEncryptedInput(contractAddress, signer.address);
input.add64(1000n);
const encrypted = await input.encrypt();
/* encrypted.handles[0] - bytes32 handle (order matches add*() call order) */
/* encrypted.inputProof - shared proof for all handles */

Decrypt Functions - Three Different Signatures

/* euint types - FhevmType IS REQUIRED */
const val: bigint = await fhevm.userDecryptEuint(
    FhevmType.euint64, handle, contractAddr, signer
);

/* ebool - NO FhevmType parameter */
const flag: boolean = await fhevm.userDecryptEbool(
    handle, contractAddr, signer
);

/* eaddress - NO FhevmType parameter */
const addr: string = await fhevm.userDecryptEaddress(
    handle, contractAddr, signer
);

This is the #1 testing mistake: adding FhevmType.ebool to userDecryptEbool by analogy with euint.

Public Decrypt - Same Pattern

const val = await fhevm.publicDecryptEuint(FhevmType.euint64, handle);
const flag = await fhevm.publicDecryptEbool(handle);
const addr = await fhevm.publicDecryptEaddress(handle);
/* No signer or contractAddress needed */

Custom Tasks

Custom Hardhat tasks MUST call await fhevm.initializeCLIApi() before using the fhevm API. Tests auto-initialize - only tasks need this.

Never Use in Tests

• fhevmjs - deprecated, use @fhevm/hardhat-plugin
• @fhevm/sdk - does not exist
• fhevm.createInstance() - exists on the implementation class but NOT on the public typed HardhatFhevmRuntimeEnvironment interface; use fhevm.createEncryptedInput() directly