Rigorous ORC integration tests

[Jefffrey]

Integration tests added by #65

However we have to compare actual vs expected data in JSON format since that is how it is encoded in the Apache ORC repo

An alternative way could be to use the pyarrow/arrow ORC implementation to generate the expected files into a parquet or arrow flight file format which can be more rigorous than JSON

We lose visibility on the expected data a bit but since these are integration tests with data from Apache ORC repo, they wouldn't change often (if at all) anyway

[Jefffrey]

Almost done, just want to optimize this code:

datafusion-orc/tests/integration/main.rs

Lines 27 to 38 in fd23fdb

	// TODO: better way of checking equality? this step is slow for zlib
	let formatted_actual = pretty::pretty_format_batches(&actual_batches)
	.unwrap()
	.to_string();
	let actual_lines = formatted_actual.trim().lines().collect::<Vec<_>>();
	let formatted_expected = pretty::pretty_format_batches(&expected_batches)
	.unwrap()
	.to_string();
	let expected_lines = formatted_expected.trim().lines().collect::<Vec<_>>();
	// TODO: Also test schema? Ignore nullability however?
	assert_eq!(actual_lines, expected_lines);

Because it is major slowdown for the zlib test

[Jefffrey]

0405e23

This commit introduces concatenating the vec of recordbatches into single recordbatch for easier comparison.

Had to disable 2 other tests due to some schema issues, but will work on that separately. Closing this issue