extract mode "1" to its own test

Tests/test_lib_image.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import itertools
+
 import pytest
 
 from PIL import Image
@@ -44,7 +46,24 @@ def test_equal(mode):
     assert img_a.im == img_b.im
 
 
-@pytest.mark.parametrize("mode", Image.MODES)
+# With mode "1" different bytes can map to the same value,
+# so we have to be more specific with the values we use.
+@pytest.mark.parametrize(
+    "bytes_a, bytes_b",
+    itertools.permutations(
+        (bytes(x) for x in itertools.product(b"\x00\xff", repeat=4)), 2
+    ),
+)
+def test_not_equal_mode_1(bytes_a, bytes_b):
+    # Use rawmode "1;8" so that each full byte is interpreted as a value
+    # instead of the bits in the bytes being interpreted as values.
+    img_a = Image.frombytes("1", (2, 2), bytes_a, "raw", "1;8")
+    img_b = Image.frombytes("1", (2, 2), bytes_b, "raw", "1;8")
+    assert img_a.tobytes() != img_b.tobytes()
+    assert img_a.im != img_b.im
+
+
+@pytest.mark.parametrize("mode", [mode for mode in Image.MODES if mode != "1"])
 def test_not_equal(mode):
     num_img_bytes = len(Image.new(mode, (2, 2)).tobytes())
     data_a = bytes(range(ord("A"), ord("A") + num_img_bytes))