code: def test_fastai_unet_train(camvid_ds, backbone):
      train_ds, valid_ds = camvid_ds
      train_dl = models.fastai.unet.train_dl(
          train_ds, batch_size=4, num_workers=0, shuffle=False
      )
      valid_dl = models.fastai.unet.valid_dl(
          valid_ds, batch_size=1, num_workers=0, shuffle=False
      )
      model = models.fastai.unet.model(
          num_classes=32,
          img_size=64,
          backbone=backbone(pretrained=True),
      )
  
      learn = models.fastai.unet.fastai.learner(
          dls=[train_dl, valid_dl], model=model
      )
  
      learn.fine_tune(1, 1e-4)
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_fastai_unet_train(camvid_ds, backbone) without return types