tests/test-mdiff.py

rust: speed up zstd decompression by re-using the decompression context

Admittedly, zstd is already pretty fast, but this change makes it
a bit faster yet: it saves ~5% of time it takes to read our large repo.

The actual motivating use case is treemanifest: in treemanifest
we end up reading *lots* of small directories, and many of them
need decompression, and there the saving for [rhg files] is >10%.
(which also seems unreasonable, we should probably keep things uncompressed more)

import unittest

from mercurial import mdiff


class splitnewlinesTests(unittest.TestCase):
    def test_splitnewlines(self):
        cases = {
            b'a\nb\nc\n': [b'a\n', b'b\n', b'c\n'],
            b'a\nb\nc': [b'a\n', b'b\n', b'c'],
            b'a\nb\nc\n\n': [b'a\n', b'b\n', b'c\n', b'\n'],
            b'': [],
            b'abcabc': [b'abcabc'],
        }
        for inp, want in cases.items():
            self.assertEqual(mdiff.splitnewlines(inp), want)


if __name__ == '__main__':
    import silenttestrunner

    silenttestrunner.main(__name__)