docstr: Multiple emitter callbacks
docstr_tok: ["Multiple","emitter","callbacks"]
code: def test_multiple_callbacks(self):
      """Multiple emitter callbacks"""
      em = EventEmitter(type="test_event")
      em.connect(functools.partial(self.record_event, key=1))
      em.connect(functools.partial(self.record_event, key=2))
      em.connect(functools.partial(self.record_event, key=3))
      ev = em()
      self.assert_result(key=1, event=ev, sources=[None])
      self.assert_result(key=2, event=ev, sources=[None])
      self.assert_result(key=3, event=ev, sources=[None])
  
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 15 for calling the TestEmitters obj's underlying member method code with example usage: obj.test_multiple_callbacks() without return types