FAILED tests/test_module_attributes.py::TestModuleAttributes::test_features fails with --system-zstd

python3 setup.py test --system-zstd
...
self = <tests.test_module_attributes.TestModuleAttributes testMethod=test_features>

    def test_features(self):
        self.assertIsInstance(zstd.backend_features, set)
    
        expected = {
            "cext": {
                "buffer_types",
                "multi_compress_to_buffer",
                "multi_decompress_to_buffer",
            },
            "cffi": set(),
            "rust": {
                "buffer_types",
                "multi_compress_to_buffer",
                "multi_decompress_to_buffer",
            },
        }[zstd.backend]
    
>       self.assertEqual(zstd.backend_features, expected)
E       AssertionError: Items in the second set but not the first:
E       'multi_compress_to_buffer'
E       'multi_decompress_to_buffer'

tests/test_module_attributes.py:29: AssertionError

I guess the tested features are available only with a statically linked copy of libzstd, right? The tests should reflect that.

Start with tests/test_module_attributes.py::TestModuleAttributes::test_features and reproduce the failure using python3 setup.py test --system-zstd. Compare the reported backend features with the system-zstd configuration, then update the test expectations so they match supported features and confirm the test suite passes.