docstr: Symbolic callbacks
docstr_tok: ["Symbolic","callbacks"]
code: def test_symbolic_callback(self):
      """Symbolic callbacks"""
      em = EventEmitter(type="test_event")
      em.connect((self, "record_event"))
      ev = em()
      self.assert_result(event=ev)
  
      # now check overriding the connected method
      def cb(ev):
          self.result = 1
  
      self.result = None
      orig_method = self.record_event
      try:
          self.record_event = cb
          em()
          assert self.result == 1
      finally:
          self.record_event = orig_method
  
imports: import unittest
  import copy
  import functools
  from vispy.util.event import Event, EventEmitter
  from vispy.testing import run_tests_if_main, assert_raises, assert_equal
label_desc: Use image node_id 16 for calling the TestEmitters obj's underlying member method code with example usage: obj.test_symbolic_callback() without return types