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

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

describe('action DISPLAY_WARNING', function () {
  it('sets appState.warning to provided value', function () {
    const initialState = {
      appState: {},
    };
    freeze(initialState);

    const warningText = 'This is a sample warning message';

    const action = actions.displayWarning(warningText);
    const resultingState = reducers(initialState, action);

    assert.equal(
      resultingState.appState.warning,
      warningText,
      'warning text set',
    );
  });
});