class_docstr: These test cases exercise the interface to the proto plan
  generation but do not call Spark.
class_docstr_tok: ["These","test","cases","exercise","the","interface","to","the","proto","plan","generation","but","do","not","call","Spark","."]
code: def test_describe(self):
      df = self.connect.readTable(table_name=self.tbl_name)
      plan = (
          df.filter(df.col_name > 3)
          .describe()
          ._plan.to_proto(self.connect)
      )
      self.assertEqual(plan.root.describe.cols, [])
  
      plan = (
          df.filter(df.col_name > 3)
          .describe("col_a", "col_b")
          ._plan.to_proto(self.connect)
      )
      self.assertEqual(
          plan.root.describe.cols,
          ["col_a", "col_b"],
      )
  
imports: import unittest
  import uuid
  import datetime
  import decimal
  import math
  from pyspark.testing.connectutils import PlanOnlyTestFixture, should_test_connect, connect_requirement_message
  from pyspark.errors import PySparkValueError
label_desc: Use image node_id 16 for calling the SparkConnectPlanTests obj's underlying member method code with example usage: obj.test_describe() without return types