code: def test_error(self):
      signals = np.random.rand(10)
      # Unsupported type.
      with self.assertRaises(ValueError):
          dct_ops.dct(signals, type=5)
      # Invalid n.
      with self.assertRaises(ValueError):
          dct_ops.dct(signals, n=-2)
      # DCT-I normalization not implemented.
      with self.assertRaises(ValueError):
          dct_ops.dct(signals, type=1, norm="ortho")
      # DCT-I requires at least two inputs.
      with self.assertRaises(ValueError):
          dct_ops.dct(np.random.rand(1), type=1)
      # Unknown normalization.
      with self.assertRaises(ValueError):
          dct_ops.dct(signals, norm="bad")
      with self.assertRaises(NotImplementedError):
          dct_ops.dct(signals, axis=0)
  
imports: import importlib
  import itertools
  from absl.testing import parameterized
  import numpy
  from tensorflow.python.eager import def_function
  from tensorflow.python.framework import tensor_spec
  from tensorflow.python.framework import test_util
  from tensorflow.python.ops.signal import dct_ops
  from tensorflow.python.platform import test
  from tensorflow.python.platform import tf_logging
label_desc: Use image node_id 4 for calling the DCTOpsTest obj's underlying member method code with example usage: obj.test_error() without return types