code: def test_validate_mode(self):
      self.assert_eq(validate_mode("a"), "append")
      self.assert_eq(validate_mode("w"), "overwrite")
      self.assert_eq(validate_mode("a+"), "append")
      self.assert_eq(validate_mode("w+"), "overwrite")
  
      with self.assertRaises(ValueError):
          validate_mode("r")
  
imports: import pandas
  from pyspark.pandas.indexes.base import Index
  from pyspark.pandas.utils import lazy_property, validate_arguments_and_invoke_function, validate_bool_kwarg, validate_index_loc, validate_mode
  from pyspark.testing.pandasutils import PandasOnSparkTestCase, _assert_pandas_equal, _assert_pandas_almost_equal
  from pyspark.testing.sqlutils import SQLTestUtils
  from pyspark.errors import PySparkAssertionError
label_desc: Use image node_id 6 for calling the UtilsTestsMixin obj's underlying member method code with example usage: obj.test_validate_mode() without return types