From a9e6da0a1ed17107f10de99aa28727500f8dad29 Mon Sep 17 00:00:00 2001
From: ptweezy <ptweezy@cronstable.dev>
Date: Tue, 27 Oct 2026 16:12:02 -0400
Subject: [PATCH] Test that IGzipFile compresses with isal_zlib at the given
 level

When IGzipFile.__init__ does not set self.compress, GzipFile compresses with zlib instead, and the igzip tests still passed.
---
 tests/test_igzip.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/tests/test_igzip.py b/tests/test_igzip.py
index b31adb85..ff87fabb 100644
--- a/tests/test_igzip.py
+++ b/tests/test_igzip.py
@@ -43,6 +43,23 @@ def test_repr(tmp_path):
         assert "<igzip _io.BufferedWriter name='" in repr(test)
 
 
+@pytest.mark.parametrize("level", range(4))
+def test_igzipfile_compresses_with_isal_zlib(level):
+    # 30,000 bytes fit in the write buffer that GzipFile has on Python 3.12
+    # and later (32 KiB or more), so IGzipFile compresses them with one
+    # compress() call.
+    with gzip.open(TEST_FILE, "rb") as f:
+        data = f.read(30_000)
+    buffer = io.BytesIO()
+    with igzip.IGzipFile(fileobj=buffer, mode="wb", compresslevel=level,
+                         mtime=0) as f:
+        f.write(data)
+    compressor = isal_zlib.compressobj(level, wbits=-isal_zlib.MAX_WBITS)
+    expected = compressor.compress(data) + compressor.flush()
+    # Leave out the 10-byte header and the 8-byte trailer.
+    assert buffer.getvalue()[10:-8] == expected
+
+
 def test_write_readonly_file():
     with igzip.IGzipFile(TEST_FILE, "rb") as test:
         with pytest.raises(OSError) as error: