Add tests and fix some issues

Tests taken from  #6360

IPython/html/services/sessions/sessionmanager.py

@@ -189,7 +189,10 b' class SessionManager(LoggingConfigurable):'
         """Takes sqlite database session row and turns it into a dictionary"""
         if row['kernel_id'] not in self.kernel_manager:
             # The kernel was killed or died without deleting the session.
-            self.delete_session(row['session_id'])
+            # We can't use delete_session here because that tries to find
+            # and shut down the kernel.
+            self.cursor.execute("DELETE FROM session WHERE session_id=?", 
+                                (row['session_id'],))
             raise KeyError
 
         model = {
@@ -207,7 +210,9 b' class SessionManager(LoggingConfigurable):'
         the session database"""
         c = self.cursor.execute("SELECT * FROM session")
         result = []
-        for row in c:
+        # We need to use fetchall() here, because row_to_model can delete rows,
+        # which messes up the cursor if we're iterating over rows.
+        for row in c.fetchall():
             try:
                 result.append(self.row_to_model(row))
             except KeyError:

IPython/html/services/sessions/tests/test_sessionmanager.py

@@ -47,6 +47,17 b' class TestSessionManager(TestCase):'
                                        kernel_name='foo')['id']
         self.assertRaises(TypeError, sm.get_session, bad_id=session_id) # Bad keyword
 
+    def test_get_session_dead_kernel(self):
+        sm = SessionManager(kernel_manager=DummyMKM())
+        session = sm.create_session(name='test1.ipynb', path='/path/to/1/', kernel_name='python')
+        # kill the kernel
+        sm.kernel_manager.shutdown_kernel(session['kernel']['id'])
+        with self.assertRaises(KeyError):
+            sm.get_session(session_id=session['id'])
+        # no sessions left
+        listed = sm.list_sessions()
+        self.assertEqual(listed, [])
+
     def test_list_sessions(self):
         sm = SessionManager(kernel_manager=DummyMKM())
         sessions = [
@@ -63,6 +74,30 b' class TestSessionManager(TestCase):'
                     'path': u'/path/to/3/'}, 'kernel':{'id':u'C', 'name':'python'}}]
         self.assertEqual(sessions, expected)
 
+    def test_list_sessions_dead_kernel(self):
+        sm = SessionManager(kernel_manager=DummyMKM())
+        sessions = [
+            sm.create_session(name='test1.ipynb', path='/path/to/1/', kernel_name='python'),
+            sm.create_session(name='test2.ipynb', path='/path/to/2/', kernel_name='python'),
+        ]
+        # kill one of the kernels
+        sm.kernel_manager.shutdown_kernel(sessions[0]['kernel']['id'])
+        listed = sm.list_sessions()
+        expected = [
+            {
+                'id': sessions[1]['id'],
+                'notebook': {
+                    'name': u'test2.ipynb',
+                    'path': u'/path/to/2/',
+                },
+                'kernel': {
+                    'id': u'B',
+                    'name':'python',
+                }
+            }
+        ]
+        self.assertEqual(listed, expected)
+
     def test_update_session(self):
         sm = SessionManager(kernel_manager=DummyMKM())
         session_id = sm.create_session(name='test.ipynb', path='/path/to/',