code: def testPredictionsNegative(self):
      labels = np.asarray([1, 1, 0, 2, 2], dtype=np.int32)
      predictions = np.asarray([2, 1, 0, -1, -1], dtype=np.int32)
      with self.assertRaisesOpError("`predictions`.*negative values"):
          self._testConfMatrix(
              labels=labels,
              predictions=predictions,
              num_classes=3,
              truth=None,
          )
  
imports: import numpy
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import errors_impl
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import confusion_matrix
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import random_ops
  from tensorflow.python.platform import test
label_desc: Use image node_id 19 for calling the ConfusionMatrixTest obj's underlying member method code with example usage: obj.testPredictionsNegative() without return types