code: def test_series_register(self):
      with ensure_removed(ps.Series, "test"):
          register_series_accessor("test")(CustomAccessor)
          assert self.psdf.a.test.prop == "item"
          assert self.psdf.a.test.method() == "item"
          assert self.psdf.a.test.check_length() == len(self.psdf["a"])
  
imports: import contextlib
  import numpy
  import pandas
  from pyspark import pandas
  from pyspark.testing.pandasutils import assert_produces_warning, ComparisonTestBase
  from pyspark.pandas.extensions import register_dataframe_accessor, register_series_accessor, register_index_accessor
label_desc: Use image node_id 5 for calling the ExtensionTestsMixin obj's underlying member method code with example usage: obj.test_series_register() without return types