added missing test file

+/*global casper*/
+/*jshint strict:false maxstatements:99*/
+var pagestack = require('pagestack');
+var utils = require('utils');
+var webpage = require('webpage');
+
+casper.test.begin('pagestack module tests', 14, function(test) {
+    var stack = pagestack.create();
+    var page1 = webpage.create();
+    page1.url = 'page1.html';
+    stack.push(page1);
+    test.assertEquals(stack.length, 1);
+    test.assert(utils.isWebPage(stack[0]));
+    test.assertEquals(stack[0], page1);
+    test.assertEquals(stack.list().length, 1);
+    test.assertEquals(stack.list()[0], page1.url);
+
+    var page2 = webpage.create();
+    page2.url = 'page2.html';
+    stack.push(page2);
+    test.assertEquals(stack.length, 2);
+    test.assert(utils.isWebPage(stack[1]));
+    test.assertEquals(stack[1], page2);
+    test.assertEquals(stack.list().length, 2);
+    test.assertEquals(stack.list()[1], page2.url);
+
+    test.assertEquals(stack.clean(page1), 1);
+    test.assertEquals(stack[0], page2);
+    test.assertEquals(stack.list().length, 1);
+    test.assertEquals(stack.list()[0], page2.url);
+
+    test.done();
+});