Cannot collect test class 'TestingDataset' warning

[mcgibbon]

The following warning displays when running our tests:

/home/mcgibbon/python/ace/fme/core/dataset/testing.py:14: PytestCollectionWarning: cannot collect test class 'TestingDataset' because it has a
     __init__ constructor (from: fme/core/dataset/test_subset.py)
         class TestingDataset(DatasetABC):

We should refactor TestingDataset to have a name that does not start or end with Test, which is a trigger for pytest to think the class is a test case class.