don't delete casper instance on shutdown test

a lunch conversation with @minrk and @takluyver lead me to just make a
popup and have it be closed, instead of having to reorder the test suite
so that this test always runs last. Now it doesn't matter what order the
test suite runs in, and gives us a pattern for testing window closing
behavior should we need it elsewhere.

IPython/html/tests/casperjs/test_cases/shutdown_notebook.js

@@ -8,25 +8,39 b' casper.notebook_test(function () {'
     //      to just test.
     //this.test.begin("shutdown tests (notebook)", 2, function(test) {
 
-    this.thenEvaluate(function () {
-        $('#kill_and_exit').click();
-    });
-    
-    this.thenEvaluate(function () {
-        var cell = IPython.notebook.get_cell(0);
-        cell.set_text('a=10; print(a)');
-        cell.execute();
-    });
+    // Our shutdown test closes the browser window, which will delete the
+    // casper browser object, and the rest of the test suite will fail with
+    // errors that look like:
+    //
+    //   "Error: cannot access member `evaluate' of deleted QObject"
+    //
+    // So what we do here is make a quick popup window, and run the test inside
+    // of it.
+    this.then(function() {
+        this.evaluate(function(url){
+            window.open(url);
+        }, {url : this.getCurrentUrl()});
+    })
 
-    // refactor this into  just a get_output(0)
-    this.then(function () {
-        var result = this.get_output_cell(0);
-        this.test.assertFalsy(result, "after shutdown: no execution results");
-        this.test.assertNot(this.kernel_running(), 
-            'after shutdown: IPython.notebook.kernel.running is false ');
-    });
+    this.waitForPopup('');
+    this.withPopup('', function () {
+        this.thenEvaluate(function () {
+            $('#kill_and_exit').click();
+        });
 
-    this.thenOpen(this.get_notebook_server());
+        this.thenEvaluate(function () {
+            var cell = IPython.notebook.get_cell(0);
+            cell.set_text('a=10; print(a)');
+            cell.execute();
+        });
+
+        this.then(function () {
+            var result = this.get_output_cell(0);
+            this.test.assertFalsy(result, "after shutdown: no execution results");
+            this.test.assertNot(this.kernel_running(),
+                'after shutdown: IPython.notebook.kernel.running is false ');
+        });
+    });
 
 //}); // end of test.begin
 });