metamask-extension/test/unit/actions/set_selected_account_test.js

const assert = require('assert')
const freeze = require('deep-freeze-strict')
const path = require('path')

const actions = require(path.join(__dirname, '..', '..', '..', 'ui', 'app', 'store', 'actions.js'))
const reducers = require(path.join(__dirname, '..', '..', '..', 'ui', 'app', 'ducks', 'index.js'))

describe('SHOW_ACCOUNT_DETAIL', function () {
  it('updates metamask state', function () {
    const initialState = {
      metamask: {
        selectedAddress: 'foo',
      },
    }
    freeze(initialState)

    const action = {
      type: actions.SHOW_ACCOUNT_DETAIL,
      value: 'bar',
    }
    freeze(action)

    const resultingState = reducers(initialState, action)
    assert.equal(resultingState.metamask.selectedAddress, action.value)
  })
})