code: def test_fpn(backbone):
      _test_none_shape(FPN, backbone, encoder_weights=None)
  
      _test_none_shape(FPN, backbone, encoder_weights="imagenet")
  
      _test_shape(
          FPN, backbone, input_shape=(256, 256, 4), encoder_weights=None
      )
  
file_path: segmentation_models/tests/test_models.py
imports: import os
  import pytest
  import random
  import six
  import numpy
  import segmentation_models
  from segmentation_models import Unet
  from segmentation_models import Linknet
  from segmentation_models import PSPNet
  from segmentation_models import FPN
  from segmentation_models import get_available_backbone_names
label_desc: Use image node_id 9 for calling a global function with example usage: test_fpn(backbone) without return types