@eth-optimism/smock

smock is a utility package that can generate mock Solidity contracts (for testing). smock hooks into a ethereumjs-vm instance so that mock contract functions can be written entirely in JavaScript. smock currently only supports Hardhat, but will be extended to support other testing frameworks.

Some nice benefits of hooking in at the VM level:

• Don't need to deploy any special contracts just for mocking!
• All of the calls are synchronous.
• Perform arbitrary javascript logic within your return value (return a function).
• It sounds cool.

smock also contains smoddit, another utility that allows you to modify the internal storage of contracts. We've found this to be quite useful in cases where many interactions occur within a single contract (typically to save gas).

Installation

You can easily install smock via npm:

npm install @eth-optimism/smock

Or via yarn:

yarn add @eth-optimism/smock

Note on Using smoddit

smoddit requires access to the internal storage layout of your smart contracts. The Solidity compiler exposes this via the storageLayout flag, which you need to enable at your hardhat config.

Here's an example hardhat.config.ts that shows how to import the plugin:

// hardhat.config.ts
import { HardhatUserConfig } from 'hardhat/config'

const config: HardhatUserConfig = {
  ...,
  solidity: {
    version: '0.7.0',
    settings: {
      outputSelection: {
        "*": {
            "*": ["storageLayout"],
        },
      },
    }
  },
}

export default config

API

Functions

smockit

Import

import { smockit } from '@eth-optimism/smock'

Signature

const smockit = async (
  spec: ContractInterface | Contract | ContractFactory,
  opts: {
    provider?: any,
    address?: string,
  },
): Promise<MockContract>

smoddit

Import

import { smoddit } from '@eth-optimism/smock'

Signature

const smoddit = async (
  name: string,
  signer?: any
): Promise<ModifiableContractFactory>

Types

smockit

MockContract

interface MockContract extends ethers.Contract {
  smocked: {
    [functionName: string]: MockContractFunction
  }

  // A wallet you can use to send transactions *from* a smocked contract
  wallet: ethers.Signer
}

MockContractFunction

interface MockContractFunction {
  calls: string[]
  will: {
    return: {
      (): void
      with: (returnValue?: MockReturnValue) => void
    }
    revert: {
      (): void
      with: (revertValue?: string) => void
    }
    resolve: 'return' | 'revert'
  }
}

MockReturnValue

export type MockReturnValue =
  | string
  | Object
  | any[]
  | ((...params: any[]) => MockReturnValue)

smoddit

ModifiableContractFactory

interface ModifiableContractFactory extends ethers.ContractFactory {
  deploy: (...args: any[]) => Promise<ModifiableContract>
}

ModifiableContract

interface ModifiableContract extends ethers.Contract {
  smodify: {
    put: (storage: any) => Promise<void>
  }
}

Examples (smockit)

Via ethers.Contract

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const MyContractFactory = await ethers.getContractFactory('MyContract')
const MyContract = await MyContractFactory.deploy(...)

// Smockit!
const MyMockContract = await smockit(MyContract)

MyMockContract.smocked.myFunction.will.return.with('Some return value!')

console.log(await MyMockContract.myFunction()) // 'Some return value!'

Asserting Call Count

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const MyContractFactory = await ethers.getContractFactory('MyContract')
const MyContract = await MyContractFactory.deploy(...)

const MyOtherContractFactory = await ethers.getContractFactory('MyOtherContract')
const MyOtherContract = await MyOtherContract.deploy(...)

// Smockit!
const MyMockContract = await smockit(MyContract)

MyMockContract.smocked.myFunction.will.return.with('Some return value!')

// Assuming that MyOtherContract.myOtherFunction calls MyContract.myFunction.
await MyOtherContract.myOtherFunction()

console.log(MyMockContract.smocked.myFunction.calls.length) // 1

Asserting Call Data

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const MyContractFactory = await ethers.getContractFactory('MyContract')
const MyContract = await MyContractFactory.deploy(...)

const MyOtherContractFactory = await ethers.getContractFactory('MyOtherContract')
const MyOtherContract = await MyOtherContract.deploy(...)

// Smockit!
const MyMockContract = await smockit(MyContract)

MyMockContract.smocked.myFunction.will.return.with('Some return value!')

// Assuming that MyOtherContract.myOtherFunction calls MyContract.myFunction with 'Hello World!'.
await MyOtherContract.myOtherFunction()

console.log(MyMockContract.smocked.myFunction.calls[0]) // 'Hello World!'

Returning (w/o Data)

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const MyContractFactory = await ethers.getContractFactory('MyContract')
const MyContract = await MyContractFactory.deploy(...)

// Smockit!
const MyMockContract = await smockit(MyContract)

MyMockContract.smocked.myFunction.will.return()

console.log(await MyMockContract.myFunction()) // []

Returning a Struct

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const MyContractFactory = await ethers.getContractFactory('MyContract')
const MyContract = await MyContractFactory.deploy(...)

// Smockit!
const MyMockContract = await smockit(MyContract)

MyMockContract.smocked.myFunction.will.return.with({
    valueA: 'Some value',
    valueB: 1234,
    valueC: true
})

console.log(await MyMockContract.myFunction()) // ['Some value', 1234, true]

Returning a Multiple Arrays

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const MyContractFactory = await ethers.getContractFactory('MyContract')
const MyContract = await MyContractFactory.deploy(...)

// Smockit!
const MyMockContract = await smockit(MyContract)

MyMockContract.smocked.myFunction.will.return.with([
  [1234, 5678],
  [4321, 8765]
])

console.log(await MyMockContract.myFunction()) // [ [1234, 5678], [4321, 8765] ]

Returning a Function

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const MyContractFactory = await ethers.getContractFactory('MyContract')
const MyContract = await MyContractFactory.deploy(...)

// Smockit!
const MyMockContract = await smockit(MyContract)

MyMockContract.smocked.myFunction.will.return.with(() => {
  return 'Some return value!'
})

console.log(await MyMockContract.myFunction()) // 'Some return value!'

Returning a Function (w/ Arguments)

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const MyContractFactory = await ethers.getContractFactory('MyContract')
const MyContract = await MyContractFactory.deploy(...)

// Smockit!
const MyMockContract = await smockit(MyContract)

MyMockContract.smocked.myFunction.will.return.with((myFunctionArgument: string) => {
  return myFunctionArgument
})

console.log(await MyMockContract.myFunction('Some return value!')) // 'Some return value!'

Reverting (w/o Data)

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const MyContractFactory = await ethers.getContractFactory('MyContract')
const MyContract = await MyContractFactory.deploy(...)

// Smockit!
const MyMockContract = await smockit(MyContract)

MyMockContract.smocked.myFunction.will.revert()

console.log(await MyMockContract.myFunction()) // Revert!

Reverting (w/ Data)

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const MyContractFactory = await ethers.getContractFactory('MyContract')
const MyContract = await MyContractFactory.deploy(...)

// Smockit!
const MyMockContract = await smockit(MyContract)

MyMockContract.smocked.myFunction.will.revert.with('0x1234')

console.log(await MyMockContract.myFunction('Some return value!')) // Revert!

Sending transactions from a smocked contract

import { ethers } from 'hardhat'
import { smockit } from '@eth-optimism/smock'

const myContractFactory = await ethers.getContractFactory('MyContract')
const myContract = await myContractFactory.deploy(...)

// Smockit!
const mock = await smockit('AnotherContract')

await myContract.connect(mock.wallet).doSomeFunction() // msg.sender == mock.address

Examples (smoddit)

Creating a Modifiable Contract

import { ethers } from 'hardhat'
import { smoddit } from '@eth-optimism/smock'

// Smoddit!
const MyModifiableContractFactory = await smoddit('MyContract')
const MyModifiableContract = await MyModifiableContractFactory.deploy(...)

Modifying a uint256

import { ethers } from 'hardhat'
import { smoddit } from '@eth-optimism/smock'

// Smoddit!
const MyModifiableContractFactory = await smoddit('MyContract')
const MyModifiableContract = await MyModifiableContractFactory.deploy(...)

await MyModifiableContract.smodify.put({
  myInternalUint256: 1234
})

console.log(await MyMockContract.getMyInternalUint256()) // 1234

Modifying a Struct

import { ethers } from 'hardhat'
import { smoddit } from '@eth-optimism/smock'

// Smoddit!
const MyModifiableContractFactory = await smoddit('MyContract')
const MyModifiableContract = await MyModifiableContractFactory.deploy(...)

await MyModifiableContract.smodify.put({
  myInternalStruct: {
    valueA: 1234,
    valueB: true
  }
})

console.log(await MyMockContract.getMyInternalStruct()) // { valueA: 1234, valueB: true }

Modifying a Mapping

import { ethers } from 'hardhat'
import { smoddit } from '@eth-optimism/smock'

// Smoddit!
const MyModifiableContractFactory = await smoddit('MyContract')
const MyModifiableContract = await MyModifiableContractFactory.deploy(...)

await MyModifiableContract.smodify.put({
  myInternalMapping: {
    1234: 5678
  }
})

console.log(await MyMockContract.getMyInternalMappingValue(1234)) // 5678

Modifying a Nested Mapping

import { ethers } from 'hardhat'
import { smoddit } from '@eth-optimism/smock'

// Smoddit!
const MyModifiableContractFactory = await smoddit('MyContract')
const MyModifiableContract = await MyModifiableContractFactory.deploy(...)

await MyModifiableContract.smodify.put({
  myInternalNestedMapping: {
    1234: {
      4321: 5678
    }
  }
})

console.log(await MyMockContract.getMyInternalNestedMappingValue(1234, 4321)) // 5678