helper.js

// `name`: The image filename
// `done`: A function provided by jasmine to invoke when we're finished
//   rendering
window.renderScreen = function renderScreen(name, done) {
  setTimeout(function() {
    window.top.callPhantom({ type: 'render', name: name });
    done();
  }, 500);
}

beforeEach(function() {
  this.container = document.createElement('div');
  this.container.style.width = '100%';
  this.container.style.border = '1px solid gray';
  this.container.style.padding = '10px';
  this.container.style.backgroundColor = 'white';
  this.container.style.boxSizing = 'border-box';
  document.body.appendChild(this.container);
});

afterEach(function() {
  this.container.remove();
});