Metamocks

a utility to mock metamask mainly for e2e testing like cypress

installation

npm i metamocks

or

yarn add metamocks

usage with cypress

add these to cypress support/commands.js file:

import {JsonRpcProvider} from '@ethersproject/providers'
import {Wallet} from '@ethersproject/wallet'
import MetaMocks from 'metamocks'

const TEST_PRIVATE_KEY = '0xe580410d7c37d26c6ad1a837bbae46bc27f9066a466fb3a66e770523b4666d19'
const DEFAULT_CHAIN_ID = 5

Cypress.Commands.add('setupMetamocks', () => {
    const provider = new JsonRpcProvider(
        "https://goerli.infura.io/v3/9aa3d95b3bc440fa88ea12eaa4456161",
        DEFAULT_CHAIN_ID
    )
    const signer = new Wallet(TEST_PRIVATE_KEY, provider)
    const metamocks = new MetaMocks(signer, DEFAULT_CHAIN_ID)
    cy.wrap(metamocks).as('metamocks')
    cy.on('window:before:load', (win) => {
        win.ethereum = metamocks
    })
})

Cypress.Commands.add('registerMockContract', (...args) => {
    cy.get('@metamocks').then((metamocks) => {
        metamocks.registerMockContract(...args)
    })
})

if you are using typescript, create a metamocks.d.ts file in the cypress folder with the following content:

import MetaMocks from 'metamocks';

export interface EthereumProvider {
    on?: (...args: any[]) => void;
    removeListener?: (...args: any[]) => void;
    autoRefreshOnNetworkChange?: boolean;
}

declare global {
    namespace Cypress {
        interface Chainable {
            registerMockContract: (...args: Parameters<MetaMocks['registerMockContract']>) => void;

            setupMetamocks(): void;
        }

        interface Window {
            ethereum?: EthereumProvider;
        }
    }
    namespace Mocha {
        interface Context {
            metamocks?: MetaMocks;
        }
    }
}

now you can setup metamocks in your tests using cy.setupMetamocks() before visiting a page

mocking abis

To mock an abi, you should create an AbiHanlder class for it, and implement the mock contract methods there. An example AbiHanlders can be found here. then register that MockContract with

metamocks.registerMockContract(contractAddress, YourContractHandler)

if you are using cypress, use this.metamocks.registerMockContract or cy.registerMockContract

example usage

visit tests and this repository to see an example usage