message: Add additional test case where only the second batch size is known (from the review comment)
diff: @@ -143,6 +143,12 @@ def _test_combinations():
  cardinality.UNKNOWN),
  ("Unbatch4", lambda: dataset_ops.Dataset.range(5).batch(2, drop_remainder=True).repeat().unbatch(),
  cardinality.INFINITE),
  + ("Unbatch5",
  + lambda: dataset_ops.Dataset.zip((
  + dataset_ops.Dataset.range(4).batch(2, drop_remainder=False),
  + dataset_ops.Dataset.range(5).batch(2, drop_remainder=True),
  + )).unbatch(),
  + 4),
  ("Window1", lambda: dataset_ops.Dataset.range(5).window(
  size=2, shift=2, drop_remainder=True), 2),
  ("Window2", lambda: dataset_ops.Dataset.range(5).window(
  