code: def test_nclasses(spark_dtree):
      assert spark_dtree.nclasses() == 2, "n classes should be 2"
  
imports: import numpy
  import pyspark
  import pytest
  from pyspark.ml.classification import DecisionTreeClassificationModel
  from pyspark.sql import SparkSession
  from dtreeviz.models.spark_decision_tree import ShadowSparkTree
label_desc: Use image node_id 9 for calling a global function with example usage: test_nclasses(spark_dtree) without return types