code: def test_download_url_json(self):
      wsgi_app = application.TensorBoardWSGI([self.plugin])
      server = werkzeug_test.Client(wsgi_app, wrappers.Response)
      response = server.get(
          "/data/plugin/custom_scalars/download_data?run=%s&tag=%s"
          % ("foo", "squares/scalar_summary")
      )
      self.assertEqual(200, response.status_code)
      self.assertEqual(
          "application/json", response.headers["Content-Type"]
      )
      body = json.loads(response.get_data())
      self.assertEqual(4, len(body))
      for step, entry in enumerate(body):
          # The time stamp should be reasonable.
          self.assertGreater(entry[0], 0)
          self.assertEqual(step, entry[1])
          np.testing.assert_allclose(step * step, entry[2])
  
imports: import csv
  import io
  import json
  import os
  import numpy
  import tensorflow
  from werkzeug import test
  from werkzeug import wrappers
  from google.protobuf import json_format
  from tensorboard.backend import application
  from tensorboard import context
  from tensorboard.backend.event_processing import data_provider
  from tensorboard.backend.event_processing import plugin_event_multiplexer
  from tensorboard.plugins import base_plugin
  from tensorboard.plugins.custom_scalar import custom_scalars_plugin
  from tensorboard.plugins.custom_scalar import layout_pb2
  from tensorboard.plugins.custom_scalar import summary
  from tensorboard.plugins.scalar import scalars_plugin
  from tensorboard.plugins.scalar import summary
  from tensorboard.util import test_util
label_desc: Use image node_id 3 for calling the CustomScalarsPluginTest obj's underlying member method code with example usage: obj.test_download_url_json() without return types