code: def test_num_unique():
      labels = [[0], [0, 1], [0, 1], [2], [0, 2, 3]]
      assert num_unique_classes(labels) == 4
  
imports: from cleanlab.internal import util
  import numpy
  import pytest
  from cleanlab.internal.label_quality_utils import get_normalized_entropy
  from cleanlab.internal.multilabel_utils import int2onehot, onehot2int
  from cleanlab.internal.util import num_unique_classes, format_labels, get_missing_classes
  from cleanlab.internal.validation import assert_valid_class_labels
label_desc: Use image node_id 10 for calling a global function with example usage: test_num_unique() without return types