Add refcount check.

test/test_unpack.py

@@ -1,6 +1,7 @@
 from io import BytesIO
+import sys
 from msgpack import Unpacker, packb, OutOfData
-from pytest import raises
+from pytest import raises, mark
 
 
 def test_unpack_array_header_from_file():
@@ -15,5 +16,32 @@ def test_unpack_array_header_from_file():
         unpacker.unpack()
 
 
+@mark.skipif(not hasattr(sys, 'getrefcount'),
+             reason='sys.getrefcount() is needed to pass this test')
+def test_unpacker_hook_refcnt():
+    result = []
+
+    def hook(x):
+        result.append(x)
+        return x
+
+    basecnt = sys.getrefcount(hook)
+
+    up = Unpacker(object_pairs_hook=hook, list_hook=hook)
+
+    assert sys.getrefcount(hook) >= basecnt + 2
+
+    up.feed(packb([{}]))
+    up.feed(packb([{}]))
+    assert up.unpack() == [{}]
+    assert up.unpack() == [{}]
+    assert result == [[{}], [{}]]
+
+    del up
+
+    assert sys.getrefcount(hook) == basecnt
+
+
 if __name__ == '__main__':
     test_unpack_array_header_from_file()
+    test_unpacker_hook_refcnt()