Use monkeypatch

Tests/test_map.py

@@ -7,36 +7,30 @@
 from PIL import Image
 
 
-def test_overflow() -> None:
+def test_overflow(monkeypatch: pytest.MonkeyPatch) -> None:
     # There is the potential to overflow comparisons in map.c
     # if there are > SIZE_MAX bytes in the image or if
     # the file encodes an offset that makes
     # (offset + size(bytes)) > SIZE_MAX
 
     # Note that this image triggers the decompression bomb warning:
-    max_pixels = Image.MAX_IMAGE_PIXELS
-    Image.MAX_IMAGE_PIXELS = None
+    monkeypatch.setattr(Image, "MAX_IMAGE_PIXELS", None)
 
     # This image hits the offset test.
     with Image.open("Tests/images/l2rgb_read.bmp") as im:
         with pytest.raises((ValueError, MemoryError, OSError)):
             im.load()
 
-    Image.MAX_IMAGE_PIXELS = max_pixels
 
-
-def test_tobytes() -> None:
+def test_tobytes(monkeypatch: pytest.MonkeyPatch) -> None:
     # Note that this image triggers the decompression bomb warning:
-    max_pixels = Image.MAX_IMAGE_PIXELS
-    Image.MAX_IMAGE_PIXELS = None
+    monkeypatch.setattr(Image, "MAX_IMAGE_PIXELS", None)
 
     # Previously raised an access violation on Windows
     with Image.open("Tests/images/l2rgb_read.bmp") as im:
         with pytest.raises((ValueError, MemoryError, OSError)):
             im.tobytes()
 
-    Image.MAX_IMAGE_PIXELS = max_pixels
-
 
 @pytest.mark.skipif(sys.maxsize <= 2**32, reason="Requires 64-bit system")
 def test_ysize() -> None: