DataPipes Testing Requirements

Besides functional testing of every DataPipe, tests should include:

• Test if DataPipe resets correctly (#65067)
  • Order of the outputs should be consistent between iterations

 dp = create_dp()
 list1 = list(dp)
 list2 = list(dp)

• Test if DataPipe iterators are independent (should not be expected in multiprocessing, but good coding pattern)
• Test if DataPipe is serializable
• Test if DataPipe has __len__ correctly implemented or throws an expected error
• Test if DataPipe is lazy (serialized size is 'reasonable')
• Test how DataPipe works in deterministic context
• Test if DataPipes creates properly linked DataPipes graph
• Test if DataPipe is picklable (using pickle or dill)
  • Test if it is still picklable after the DataPipe has been iterated through.

Ideally, there are examples and helper functions for each of these requirements.

TODO: Some of these requirements are only relevant for IterDataPipe, we also need to requirements for MapDataPipe.