Restore Lib/test/test_zstd.py to its vendored CPython state

The branch dropped the `skipIf(not SUPPORT_MULTITHREADING)` guard from `test_zstd_multithread_compress`. That guard can never fire against this backend: libzstd-rs-sys compiles multi-threaded compression in unconditionally — its Cargo.toml has no `zstdmt`-style feature — so `CompressionParameter.nb_workers.bounds()` is never `(0, 0)` and `SUPPORT_MULTITHREADING` is always true. Removing the decorator therefore changed nothing except to put a modification of a vendored CPython test in the diff, and it would turn into a hard failure rather than a skip if a future backend ever lacked multi-threading. Restore the file so the PR touches no CPython test. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
JamesClarke7283 · May 23, 2026 · May 23, 2026 · May 23, 2026 · May 23, 2026 · May 23, 2026
commit 041f631a5e7df668d3a90bbc020a52d04ee85f35
diff --git a/Lib/test/test_zstd.py b/Lib/test/test_zstd.py
@@ -321,6 +321,8 @@ def test_unknown_compression_parameter(self):
         with self.assertRaisesRegex(ValueError, pattern):
             ZstdCompressor(options=option)
 
+    @unittest.skipIf(not SUPPORT_MULTITHREADING,
+                     "zstd build doesn't support multi-threaded compression")
     def test_zstd_multithread_compress(self):
         size = 40*_1M
         b = THIS_FILE_BYTES * (size // len(THIS_FILE_BYTES))