Match error message

Author: radarhere

Tests/test_file_blp.py

@@ -60,7 +60,7 @@ def test_save(tmp_path: Path) -> None:
             assert_image_similar_tofile(im, f, 8)
 
     im = hopper()
-    with pytest.raises(ValueError):
+    with pytest.raises(ValueError, match="Unsupported BLP image mode"):
         im.save(f)