code: def test_three_party(self):
      self.fl_server.set_client_num(3)
      self.fl_server.build()
      self.fl_server.start()
      mock_party1 = Process(
          target=mock_process,
          args=(
              2,
              "house-prices-train-preprocessed-1.csv",
              "house-prices-test-preprocessed-1.csv",
              self.target,
          ),
      )
      mock_party1.start()
      mock_party2 = Process(
          target=mock_process,
          args=(
              3,
              "house-prices-train-preprocessed-2.csv",
              "house-prices-test-preprocessed-2.csv",
              self.target,
          ),
      )
      mock_party2.start()
  
      df_train = pd.read_csv(
          os.path.join(
              resource_path, "house-prices-train-preprocessed-0.csv"
          )
      )
      fgboost_regression = FGBoostRegression()
      if "SalePrice" in df_train:
          df_x = df_train.drop("SalePrice", 1)
          df_y = df_train.filter(items=["SalePrice"])
  
          fgboost_regression.fit(
              df_x,
              df_y,
              feature_columns=df_x.columns,
              label_columns=["SalePrice"],
              num_round=15,
          )
      else:
          fgboost_regression.fit(
              df_train, feature_columns=df_train.columns, num_round=15
          )
  
      df_test = pd.read_csv(
          os.path.join(
              resource_path, "house-prices-test-preprocessed-0.csv"
          )
      )
      result = fgboost_regression.predict(
          df_test, feature_columns=df_test.columns
      )
      result = np.exp(result)
      assert len(result) == len(TestFGBoostRegression.xgboost_result)
      assert np.allclose(
          result, TestFGBoostRegression.xgboost_result, rtol=10, atol=10
      )
  
imports: from multiprocessing import Process
  import unittest
  from uuid import uuid4
  import numpy
  import pandas
  import os
  import math
  from bigdl.ppml.fl import *
  from bigdl.ppml.fl.algorithms.fgboost_regression import FGBoostRegression
  from bigdl.ppml.fl.fl_server import FLServer
  from bigdl.ppml.fl.utils import init_fl_context
  from bigdl.ppml.fl.utils import FLTest
label_desc: Use image node_id 6 for calling the TestFGBoostRegression obj's underlying member method code with example usage: obj.test_three_party() without return types