add e2e test for modal

test/e2e/modal.js

@@ -0,0 +1,22 @@
+casper.test.begin('modal', 8, function (test) {
+  casper
+  .start('examples/modal/index.html')
+  .then(function () {
+    test.assertNotVisible('.modal-mask')
+  })
+  .thenClick('#show-modal', function () {
+    test.assertVisible('.modal-mask')
+    test.assertVisible('.modal-wrapper')
+    test.assertVisible('.modal-container')
+    test.assertSelectorHasText('.modal-header h3', 'custom header')
+    test.assertSelectorHasText('.modal-body', 'default body')
+    test.assertSelectorHasText('.modal-footer', 'default footer')
+  })
+  .thenClick('.modal-default-button', function () {
+    test.assertNotVisible('.modal-mask')
+  })
+  // run
+  .run(function () {
+    test.done()
+  })
+})