class_docstr: Tests for `ClientFeatureFlagsMiddleware`.
class_docstr_tok: ["Tests","for","`","ClientFeatureFlagsMiddleware","`","."]
code: def _echo_app(self, environ, start_response):
      # https://www.python.org/dev/peps/pep-0333/#environ-variables
      data = {
          "client_feature_flags": context.from_environ(
              environ
          ).client_feature_flags,
      }
      body = json.dumps(data)
      start_response("200 OK", [("Content-Type", "application/json")])
      return [body]
  
imports: import json
  from werkzeug import test
  from werkzeug import wrappers
  from tensorboard import context
  from tensorboard import errors
  from tensorboard import test
  from tensorboard.backend import client_feature_flags
label_desc: Use image node_id 1 for calling the ClientFeatureFlagsMiddlewareTest obj's underlying member method code with example usage: obj._echo_app(environ, start_response) and returns: list