No way to specify dataset size via environment variable

[dchigarev]

New introduced system of handling environment variables assumes that all of the values will be in a Title Case

modin/modin/config/pubsub.py

Lines 25 to 31 in 3fd16a9

	_TYPE_PARAMS = {
	str: TypeDescriptor(
	decode=lambda value: value.strip().title(),
	normalize=lambda value: value.strip().title(),
	verify=lambda value: True,
	help="a string",
	),

However, key names in DATASET_SIZE_DICT don't follow that rule

modin/modin/pandas/test/utils.py

Lines 30 to 37 in 3fd16a9

	DATASET_SIZE_DICT = {
	"small": (2 ** 2, 2 ** 3),
	"normal": (2 ** 6, 2 ** 8),
	"big": (2 ** 7, 2 ** 12),
	}
	# Size of test dataframes
	NCOLS, NROWS = DATASET_SIZE_DICT.get(TestDatasetSize.get(), DATASET_SIZE_DICT["normal"])