[ptweezy]

When IGzipFile.__init__() doesn't set self.compress, GzipFile compresses with zlib instead, and no test checked for that. The new test compares the deflate data that IGzipFile writes at each level with the output of isal_zlib.compressobj(), byte for byte.

To test it, I removed that line, and in another copy, always passed level 2 to compressobj(). The old tests in tests/test_igzip.py and the gzip compliance tests pass in both cases. The new test fails at all four levels with the first change, and at levels 0, 1, and 3 with the second.

The test writes 30,000 bytes. They fit in the write buffer that GzipFile has on Python 3.12 and later, so IGzipFile compresses them with one compress() call, like the compressobj() call it is compared with.

This PR changes only tests, so it has no CHANGELOG entry.

Checklist

• Pull request details were added to CHANGELOG.rst
• Documentation was updated (if needed)