docstr: Test the constructor directly.
          
docstr_tok: ["Test","the","constructor","directly","."]
code: def test_init_single_channel(
      self,
      num_channels: int,
      channel_selector: Type[Union[str, int, List[int]]],
  ):
      """Test the constructor directly."""
      if num_channels == 1:
          # samples is a one-dimensional vector for single-channel signal
          samples = np.random.rand(self.num_samples)
      else:
          samples = np.random.rand(self.num_samples, num_channels)
  
      if (
          isinstance(channel_selector, int)
          and channel_selector >= num_channels
      ) or (
          isinstance(channel_selector, list)
          and max(channel_selector) >= num_channels
      ):
          # Expect a failure if looking for a different channel when input is 1D
          with pytest.raises(ValueError):
              # Construct UUT
              uut = AudioSegment(
                  samples=samples,
                  sample_rate=self.sample_rate,
                  channel_selector=channel_selector,
              )
      else:
          # Construct UUT
          uut = AudioSegment(
              samples=samples,
              sample_rate=self.sample_rate,
              channel_selector=channel_selector,
          )
  
          # Create golden reference
          # Note: AudioSegment converts input samples to float32
          golden_samples = select_channels(
              samples.astype("float32"), channel_selector
          )
          expected_num_channels = (
              1 if golden_samples.ndim == 1 else golden_samples.shape[1]
          )
  
          # Test UUT
          assert uut.num_channels == expected_num_channels
          assert uut.num_samples == self.num_samples
          assert uut.sample_rate == self.sample_rate
          assert uut.duration == self.signal_duration_sec
          max_diff = np.max(np.abs(uut.samples - golden_samples))
          assert max_diff < self.max_diff_tol
  
          # Test zero padding
          pad_length = 42
          uut.pad(pad_length, symmetric=False)
          # compare to golden references
          assert uut.num_samples == self.num_samples + pad_length
          assert np.all(uut.samples[-pad_length:] == 0.0)
          max_diff = np.max(
              np.abs(uut.samples[:-pad_length] - golden_samples)
          )
          assert max_diff < self.max_diff_tol
  
          # Test subsegment
          start_time = 0.2 * self.signal_duration_sec
          end_time = 0.5 * self.signal_duration_sec
          uut.subsegment(start_time=start_time, end_time=end_time)
          # compare to golden references
          start_sample = int(round(start_time * self.sample_rate))
          end_sample = int(round(end_time * self.sample_rate))
          max_diff = np.max(
              np.abs(
                  uut.samples - golden_samples[start_sample:end_sample]
              )
          )
          assert max_diff < self.max_diff_tol
  
file_path: NeMo/tests/collections/asr/test_preprocessing_segment.py
imports: import json
  import os
  import tempfile
  from typing import List, Type, Union
  import numpy
  import pytest
  import soundfile
  from nemo.collections.asr.parts.preprocessing.perturb import NoisePerturbation, SilencePerturbation
  from nemo.collections.asr.parts.preprocessing.segment import AudioSegment
  from nemo.collections.asr.parts.utils.audio_utils import select_channels
label_desc: Use image node_id 2 for calling the TestAudioSegment obj's underlying member method code with example usage: obj.test_init_single_channel(num_channels, channel_selector) without return types