sinon-chrome0.2.1 with PhantomJS 2.0.0 workaround for an issue where PhantomJS ignores chai's AssertionError.

beforeeach.js

// sinon-chrome (https://github.com/vitalets/sinon-chrome/blob/master/example/test/beforeeach.js)
var fs = require('fs');
var page;
var beforeLoadFn;

beforeEach(function() {
  page = require('webpage').create();
  /**
   * evaluate a function in the page
   * @param   {function}  func    the function to evaluate
   * @param   {...}       args    function arguments
   * @return  {*}                 the function call result
   */
  page.evaluate = function (func, args) {
    var str, arg, argType, i, l;
    if (!(func instanceof Function || typeof func === 'string' || func instanceof String)) {
      throw "Wrong use of WebPage#evaluate";
    }
    str = 'function() { try { return (' + func.toString() + ')(';
    for (i = 1, l = arguments.length; i < l; i++) {
      arg = arguments[i];
      argType = detectType(arg);

      switch (argType) {
      case "object":      //< for type "object"
      case "array":       //< for type "array"
          str += JSON.stringify(arg) + ","
          break;
      case "date":        //< for type "date"
          str += "new Date(" + JSON.stringify(arg) + "),"
          break;
      case "string":      //< for type "string"
          str += quoteString(arg) + ',';
          break;
      default:            // for types: "null", "number", "function", "regexp", "undefined"
          str += arg + ',';
          break;
      }
    }
    // re-throw the caught error as Error type since AssertionError type is silently ignored by phantomjs. why?
    str = str.replace(/,$/, '') + '); } catch (e) { throw new Error(e); } }';
    return this.evaluateJavaScript(str);
  };

  page.onConsoleMessage = function(msg) {
    console.log(msg);
  };

  // listen page.onError to catch assertions
  page.onError = function(msg, trace) {
    var msgStack = [msg];
    if (trace && trace.length) {
      msgStack.push('TRACE:');
      trace.forEach(function(t) {
        msgStack.push(' -> ' + t.file + ': ' + t.line + (t.function ? ' (in function "' + t.function +'")' : ''));
      });
    }
    // we need try..catch here as mocha throws error that catched by phantom.onError
    try {
      mocha.throwError(msgStack.join('\n'));
    } catch(e) { }
  };

  page.onInitialized = function() {
    page.injectJs(node_modules + 'chai/chai.js');
    page.injectJs(node_modules + 'sinon/pkg/sinon.js');
    page.injectJs(node_modules + 'sinon-chrome/chrome.js');
    page.injectJs(node_modules + 'sinon-chrome/src/phantom-tweaks.js');
    page.evaluate(function() {
      assert = chai.assert;

      // for emulating click
      clickEvent = document.createEvent('MouseEvents');
      clickEvent.initMouseEvent('click', true);
    });
    // call additional function defined in tests
    if (beforeLoadFn) {
      beforeLoadFn();
    }
  };
});

afterEach(function() {
  page.close();
  beforeLoadFn = null;
});