input: 
  def generate_voltage_signal(freq: float, amplitude: float, noise_std: float, duration: float, samples: int) -> np.ndarray:
      """
      Generate a voltage signal with random noise.
      >>> generate_voltage_signal(250, 1, 0.1, 1, 1000)
      np.ndarray([...])  # The actual array values will vary due to randomness
      """
      t = np.linspace(0, duration, samples)
      voltage_signal = amplitude * np.sin(2 * np.pi * freq * t) + np.random.normal(0, noise_std, samples)
      return voltage_signal
  
output:     t = np.linspace(0, duration, samples)
      voltage_signal = amplitude * np.sin(2 * np.pi * freq * t) + np.random.normal(0, noise_std, samples)
      return voltage_signal