docstr: Emitter constructed with no arguments
docstr_tok: ["Emitter","constructed","with","no","arguments"]
code: def test_emitter(self):
      """Emitter constructed with no arguments"""
      em = EventEmitter()
  
      # type must be specified when emitting since Event requires type
      # argument and the emitter was constructed without it.
      try:
          em()
          assert (
              False
          ), "Emitting event with no type should have failed."
      except TypeError:
          pass
  
      # See that emitted event has all of the properties we expect
      ev = self.try_emitter(em, type="test_event")
      self.assert_result(
          event=ev,
          event_class=Event,
          source=None,
          type="test_event",
          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 1 for calling the TestEmitters obj's underlying member method code with example usage: obj.test_emitter() without return types