code: def test_dataframe_register(self):
      with ensure_removed(ps.DataFrame, "test"):
          register_dataframe_accessor("test")(CustomAccessor)
          assert self.psdf.test.prop == "item"
          assert self.psdf.test.method() == "item"
          assert len(self.psdf["a"]) == self.psdf.test.check_length("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 4 for calling the ExtensionTestsMixin obj's underlying member method code with example usage: obj.test_dataframe_register() without return types