code: def test_image_unknown_len(self):
      imgs = [
          np.random.randint(256, size=(28, 28, 3), dtype=np.uint8),
          np.random.randint(256, size=(28, 28, 3), dtype=np.uint8),
      ]
      imgs_stacked = np.stack(imgs)
  
      self.assertFeature(
          feature=feature_lib.Sequence(
              feature_lib.Image(shape=(None, None, 3))
          ),
          dtype=np.uint8,
          shape=(None, None, None, 3),  # (length, h, w, c)
          tests=[
              testing.FeatureExpectationItem(
                  value=[],  # Empty input
                  expected=np.empty(shape=(0, 0, 0, 3), dtype=np.uint8),
                  expected_np=np.empty(
                      shape=(0, 0, 0, 3), dtype=np.uint8
                  ),
              ),
              testing.FeatureExpectationItem(
                  value=imgs,
                  expected=imgs_stacked,
                  expected_np=imgs_stacked,
              ),
          ],
      )
  
imports: import numpy
  import tensorflow
  from tensorflow_datasets import testing
  from tensorflow_datasets.core import features
label_desc: Use image node_id 3 for calling the SequenceFeatureTest obj's underlying member method code with example usage: obj.test_image_unknown_len() without return types