code: def test_spark_df_to_ray_dataset(orca_context_fixture):
      sc = OrcaContext.get_spark_context()
      spark = SparkSession(sc)
      spark_df = spark.createDataFrame(
          [(1, "a"), (2, "b"), (3, "c"), (4, "d")], ["one", "two"]
      )
      rows = [(r.one, r.two) for r in spark_df.take(4)]
      ds = spark_df_to_ray_dataset(spark_df)
      values = [(r["one"], r["two"]) for r in ds.take(8)]
      assert values == rows
  
imports: import pytest
  from bigdl.orca.data import spark_df_to_ray_dataset
  from bigdl.orca import OrcaContext
  from pyspark.sql import SparkSession
label_desc: Use image node_id 1 for calling a global function with example usage: test_spark_df_to_ray_dataset(orca_context_fixture) without return types