test: add Hypothesis fuzz tests for prefix and Code parsing

newsfragments/48.misc.rst

@@ -0,0 +1 @@
+Add Hypothesis-based fuzz tests so prefix and Code parsing helpers never crash on random input.

pyproject.toml

@@ -38,6 +38,7 @@ dev = [
     "bump-my-version>=1.2.0",
     "mypy",
     "pre-commit",
+    "hypothesis",
     "pytest",
     "pytest-runner",
     "ruff",

tests/test_fuzz.py

@@ -0,0 +1,41 @@
+"""Property-based / fuzz tests for parsing helpers.
+
+These tests assert that malformed or random input raises documented
+exceptions (or returns a bool) rather than crashing with unexpected errors.
+"""
+
+from hypothesis import given
+from hypothesis import strategies as st
+
+from multicodec import Code, extract_prefix, get_codec, is_codec
+
+
+@given(st.binary(max_size=100))
+def test_extract_prefix_never_crashes(data: bytes) -> None:
+    """extract_prefix should raise ValueError, not crash."""
+    try:
+        extract_prefix(data)
+    except ValueError:
+        pass
+
+
+@given(st.binary(max_size=100))
+def test_get_codec_never_crashes(data: bytes) -> None:
+    try:
+        get_codec(data)
+    except ValueError:
+        pass
+
+
+@given(st.text(max_size=100))
+def test_code_from_string_never_crashes(text: str) -> None:
+    try:
+        Code.from_string(text)
+    except ValueError:
+        pass
+
+
+@given(st.text(max_size=100))
+def test_is_codec_never_crashes(text: str) -> None:
+    result = is_codec(text)
+    assert isinstance(result, bool)