metamask-extension/test/stub/provider.js

const JsonRpcEngine = require('json-rpc-engine')
const scaffoldMiddleware = require('eth-json-rpc-middleware/scaffold')
const providerAsMiddleware = require('eth-json-rpc-middleware/providerAsMiddleware')
const GanacheCore = require('ganache-core')

module.exports = {
  createEngineForTestData,
  providerFromEngine,
  scaffoldMiddleware,
  createTestProviderTools,
  getTestSeed,
  getTestAccounts,
}

function getTestSeed () {
  return 'people carpet cluster attract ankle motor ozone mass dove original primary mask'
}

function getTestAccounts () {
  return [
    { address: '0x88bb7F89eB5e5b30D3e15a57C68DBe03C6aCCB21', key: Buffer.from('254A8D551474F35CCC816388B4ED4D20B945C96B7EB857A68064CB9E9FB2C092', 'hex') },
    { address: '0x1fe9aAB565Be19629fF4e8541ca2102fb42D7724', key: Buffer.from('6BAB5A4F2A6911AF8EE2BD32C6C05F6643AC48EF6C939CDEAAAE6B1620805A9B', 'hex') },
    { address: '0xbda5c89aa6bA1b352194291AD6822C92AbC87c7B', key: Buffer.from('9B11D7F833648F26CE94D544855558D7053ECD396E4F4563968C232C012879B0', 'hex') },
  ]
}

function createEngineForTestData () {
  return new JsonRpcEngine()
}

function providerFromEngine (engine) {
  const provider = { sendAsync: engine.handle.bind(engine) }
  return provider
}

function createTestProviderTools (opts = {}) {
  const engine = createEngineForTestData()
  // handle provided hooks
  engine.push(scaffoldMiddleware(opts.scaffold || {}))
  // handle block tracker methods
  engine.push(providerAsMiddleware(GanacheCore.provider({
    mnemonic: getTestSeed(),
  })))
  // wrap in standard provider interface
  const provider = providerFromEngine(engine)
  return { provider, engine }
}