code: def test_in_memory_data_source(self):
      class InMemDataSourceReader(DataSourceReader):
          DEFAULT_NUM_PARTITIONS: int = 3
  
          def __init__(self, options):
              self.options = options
  
          def partitions(self):
              if "num_partitions" in self.options:
                  num_partitions = int(self.options["num_partitions"])
              else:
                  num_partitions = self.DEFAULT_NUM_PARTITIONS
              return [InputPartition(i) for i in range(num_partitions)]
  
          def read(self, partition):
              yield partition.value, str(partition.value)
  
      class InMemoryDataSource(DataSource):
          @classmethod
          def name(cls):
              return "memory"
  
          def schema(self):
              return "x INT, y STRING"
  
          def reader(self, schema) -> "DataSourceReader":
              return InMemDataSourceReader(self.options)
  
      self.spark.dataSource.register(InMemoryDataSource)
      df = self.spark.read.format("memory").load()
      self.assertEqual(df.rdd.getNumPartitions(), 3)
      assertDataFrameEqual(
          df, [Row(x=0, y="0"), Row(x=1, y="1"), Row(x=2, y="2")]
      )
  
      df = (
          self.spark.read.format("memory")
          .option("num_partitions", 2)
          .load()
      )
      assertDataFrameEqual(df, [Row(x=0, y="0"), Row(x=1, y="1")])
      self.assertEqual(df.rdd.getNumPartitions(), 2)
  
imports: import os
  import tempfile
  import unittest
  from typing import Callable, Union
  from pyspark.errors import PythonException
  from pyspark.sql.datasource import DataSource, DataSourceReader, InputPartition, DataSourceWriter, WriterCommitMessage, CaseInsensitiveDict
  from pyspark.sql.types import Row, StructType
  from pyspark.testing import assertDataFrameEqual
  from pyspark.testing.sqlutils import ReusedSQLTestCase
  from pyspark.testing.utils import SPARK_HOME
label_desc: Use image node_id 16 for calling the BasePythonDataSourceTestsMixin obj's underlying member method code with example usage: obj.test_in_memory_data_source() and returns: unknown, str, str, InMemDataSourceReader