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

import assert from 'assert';
import freeze from 'deep-freeze-strict';
import reducers from '../../../ui/app/ducks';
import * as actionConstants from '../../../ui/app/store/actionConstants';

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

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

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