measureText: function(text) {
        return {
          width:  12*text.length,
          height: 14
        };
      },

var myHackedInCanvas;    // Use one global canvas instance for all calls to createElement('canvas');

function replaceCanvasContext (el) {
  // The previous export
}

/**
 * Overrides document.createElement(), in order to supply a custom canvas element.
 *
 * In the canvas element, getContext() is overridden in order to supply a simple 
 * mock object for the 2D context. For all other elements, the call functions unchanged.
 *
 * The override is only done if there is no 2D context already present.
 * This allows for normal running in a browser, and for node.js the usage of 'canvas'.
 *
 * @param {object} the current global window object. This can possibly come from module 'jsdom',
 *                 when running under node.js.
 */
function mockify(window) {
  var d = window.document;
  var f = window.document.createElement;

  // Check if 2D context already present. That happens either when running in a browser,
  // or this is node.js with 'canvas' installed. 
  var ctx = d.createElement('canvas').getContext('2d');
  if (ctx !== null && ctx !== undefined) {
    //console.log('2D context is present, no need to override');
    return;
  }

  window.document.createElement = function(param) {
    if (param === 'canvas') {
      if (myHackedInCanvas === undefined) {
        myHackedInCanvas = f.call(d, 'canvas');
        replaceCanvasContext(myHackedInCanvas);
      }
      return myHackedInCanvas;
    } else {
      return f.call(d, param);
    }
  };
}

module.exports = mockify;