message: Add test case for cardinality with Dataset.unbatch()
diff: @@ -134,6 +134,15 @@ def _test_combinations():
  lambda: dataset_ops.Dataset.range(5).filter(lambda _: True).take(2),
  cardinality.UNKNOWN),
  ("Take4", lambda: dataset_ops.Dataset.range(5).repeat().take(2), 2),
  + ("Unbatch1",
  + lambda: dataset_ops.Dataset.range(5).batch(2, drop_remainder=True).unbatch(), 4),
  + ("Unbatch2",
  + lambda: dataset_ops.Dataset.range(5).batch(2, drop_remainder=False).unbatch(), cardinality.UNKNOWN),
  + ("Unbatch3",
  + lambda: dataset_ops.Dataset.range(5).batch(2, drop_remainder=True).filter(lambda _: True).unbatch(),
  + cardinality.UNKNOWN),
  + ("Unbatch4", lambda: dataset_ops.Dataset.range(5).batch(2, drop_remainder=True).repeat().unbatch(),
  + cardinality.INFINITE),
  ("Window1", lambda: dataset_ops.Dataset.range(5).window(
  size=2, shift=2, drop_remainder=True), 2),
  ("Window2", lambda: dataset_ops.Dataset.range(5).window(
  