test: add fuzz testing using hypothesis

pyproject.toml

@@ -38,6 +38,7 @@ dev = [
     "Sphinx>=5.0.0",
     "build>=0.9.0",
     "bump-my-version>=1.2.0",
+    "hypothesis",
     "mypy",
     "pre-commit",
     "pytest",

tests/test_fuzz.py

@@ -0,0 +1,35 @@
+from hypothesis import given, settings
+from hypothesis import strategies as st
+
+from multibase import ENCODINGS, decode, encode
+
+
+@given(st.binary(max_size=200))
+@settings(max_examples=1000)
+def test_decode_never_crashes(data):
+    """decode() should raise an exception, not crash."""
+    try:
+        decode(data)
+    except Exception:
+        pass  # Any exception is fine, just no crashes
+
+
+@given(st.text(max_size=200))
+@settings(max_examples=1000)
+def test_decode_string_never_crashes(data):
+    try:
+        decode(data)
+    except Exception:
+        pass
+
+
+@given(st.binary(min_size=1, max_size=100))
+@settings(max_examples=500)
+def test_roundtrip_never_crashes(data):
+    """encode then decode should never crash."""
+    for enc in ENCODINGS:
+        try:
+            encoded = encode(enc.encoding, data)
+            decode(encoded)
+        except Exception:
+            pass