code: def test_string_find(self):
      self.check_func(lambda x: x.str.find("a"))
      self.check_func(lambda x: x.str.find("a", start=3))
      self.check_func(lambda x: x.str.find("a", start=0, end=1))
  
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 8 for calling the SeriesStringOpsAdvMixin obj's underlying member method code with example usage: obj.test_string_find() without return types