code: def test_string_pad(self):
      self.check_func(lambda x: x.str.pad(10))
      self.check_func(lambda x: x.str.pad(10, side="both"))
      self.check_func(
          lambda x: x.str.pad(10, side="right", fillchar="-")
      )
  
imports: import pandas
  import numpy
  import re
  from pyspark import pandas
  from pyspark.testing.pandasutils import PandasOnSparkTestCase
  from pyspark.testing.sqlutils import SQLTestUtils
label_desc: Use image node_id 16 for calling the SeriesStringOpsAdvMixin obj's underlying member method code with example usage: obj.test_string_pad() without return types