[core][tests][events] Remove nose

IPython/core/tests/test_events.py

@@ -1,6 +1,5 b''
 import unittest
 from unittest.mock import Mock
-import nose.tools as nt
 
 from IPython.core import events
 import IPython.testing.tools as tt
@@ -40,9 +39,9 b' class CallbackTests(unittest.TestCase):'
         def cb2():
             ...
 
-        self.em.register('ping_received', cb1)
-        nt.assert_raises(ValueError, self.em.unregister, 'ping_received', cb2)
-        self.em.unregister('ping_received', cb1)
+        self.em.register("ping_received", cb1)
+        self.assertRaises(ValueError, self.em.unregister, "ping_received", cb2)
+        self.em.unregister("ping_received", cb1)
 
     def test_cb_error(self):
         cb = Mock(side_effect=ValueError)