input: Write a function to generate a voltage signal with random noise. The function should take in the frequency and amplitude of the signal as inputs and return a time series of the voltage signal with added noise.
  
  
  def generate_voltage_signal(freq, amplitude):
      t = np.linspace(0, 1, 1000)
      voltage_signal = np.sin(2 * np.pi * freq * t) + np.random.normal(0, 0.1, 1000)
      return voltage_signal
  
  assert (generate_voltage_signal(250, 1)[0] >= -1 and generate_voltage_signal(250, 1)[0] <= 1)
  assert (np.mean(generate_voltage_signal(250, 1)[:100]) < 1)
  
output: def generate_voltage_signal(freq, amplitude):
      t = np.linspace(0, 1, 1000)
      voltage_signal = amplitude * np.sin(2 * np.pi * freq * t) + np.random.normal(0, 0.1, 1000)
      return voltage_signal