class_docstr: Tests for `plugin_util.experiment_id`.
code: def test_default(self):
      # This shouldn't happen; the `ExperimentIdMiddleware` always set an
      # experiment ID. In case something goes wrong, degrade gracefully.
      environ = {}
      self.assertEqual(plugin_util.experiment_id(environ), "")
  
imports: import textwrap
  from tensorboard import context
  from tensorboard import plugin_util
  from tensorboard import test
  from tensorboard.backend import experiment_id
label_desc: Use image node_id 1 for calling the ExperimentIdTest obj's underlying member method code with example usage: obj.test_default() without return types