code: def test_insert_in_background_intensity(self):
      intensity = audaugs.insert_in_background_intensity(
          metadata={"src_duration": 10.0, "dst_duration": 15.0}
      )
      self.assertAlmostEqual(intensity, 33.3333333)
  
imports: import unittest
  import numpy
  from augly import audio
label_desc: Use image node_id 8 for calling the IntensityAudioUnitTest obj's underlying member method code with example usage: obj.test_insert_in_background_intensity() without return types