test(tests): add RLP canonical Uint decoding test

tests/json_loader/test_rlp_canonical_uint.py

@@ -0,0 +1,45 @@
+"""
+Test that decoding RLP into `Uint` rejects non-canonical integers.
+
+Canonical RLP encodes integers without leading zero bytes, so ``0`` is
+the empty byte string rather than ``0x00``. Decoding an encoding that
+carries a leading zero must fail, otherwise the specification tooling
+would accept inputs that execution clients reject.
+
+See https://github.com/ethereum/ethereum-rlp/issues/10.
+"""
+
+import pytest
+from ethereum_rlp import rlp
+from ethereum_rlp.exceptions import DecodingError
+from ethereum_types.numeric import Uint
+
+
+@pytest.mark.parametrize(
+    "encoded, expected",
+    [
+        pytest.param(b"\x80", 0, id="zero-empty-string"),
+        pytest.param(b"\x01", 1, id="one"),
+        pytest.param(b"\x7f", 0x7F, id="single-byte-max"),
+        pytest.param(b"\x82\x01\x00", 0x0100, id="two-bytes"),
+    ],
+)
+def test_decode_to_uint_accepts_canonical(
+    encoded: bytes, expected: int
+) -> None:
+    """Decode canonical `Uint` encodings with no leading zero byte."""
+    assert rlp.decode_to(Uint, encoded) == Uint(expected)
+
+
+@pytest.mark.parametrize(
+    "encoded",
+    [
+        pytest.param(b"\x00", id="single-zero-byte"),
+        pytest.param(b"\x82\x00\x01", id="leading-zero-two-bytes"),
+        pytest.param(b"\x83\x00\x00\x01", id="leading-zeros-three-bytes"),
+    ],
+)
+def test_decode_to_uint_rejects_leading_zeros(encoded: bytes) -> None:
+    """Reject `Uint` encodings that carry a non-canonical leading zero."""
+    with pytest.raises(DecodingError, match="non-canonical"):
+        rlp.decode_to(Uint, encoded)