docstr: Assert there is exactly one DebuggerV2 run and get its ID.
docstr_tok: ["Assert","there","is","exactly","one","DebuggerV2","run","and","get","its","ID","."]
code: def _getExactlyOneRun(self):
      """Assert there is exactly one DebuggerV2 run and get its ID."""
      run_listing = json.loads(
          self.server.get(_ROUTE_PREFIX + "/runs").get_data()
      )
      self.assertLen(run_listing, 1)
      return list(run_listing.keys())[0]
  
imports: import collections
  import json
  import os
  import socket
  import threading
  import tensorflow
  from werkzeug import test
  from werkzeug import wrappers
  from tensorboard.backend import application
  from tensorboard.plugins import base_plugin
  from tensorboard.plugins.debugger_v2 import debug_data_multiplexer
  from tensorboard.plugins.debugger_v2 import debugger_v2_plugin
label_desc: Use image node_id 3 for calling the DebuggerV2PluginTest obj's underlying member method code with example usage: obj._getExactlyOneRun() and returns: list