Add fuzz testing for prefix operations and `Code` parsing

[sumanjeet0012]

There is no fuzz testing for extract_prefix(), get_codec(), Code.from_string(), or other parsing functions. go-multicodec includes a fuzz target that exercises Cast(), String(), Prefix(), and JSON round-trips with random input.

Problem

Parsing functions like extract_prefix() and Code.from_string() accept arbitrary input but are only tested with valid or specifically-crafted invalid inputs. Random/malformed input could trigger unhandled exceptions, infinite loops, or excessive memory allocation.

go-multicodec has a fuzz target (cid_fuzz.go) that:

func Fuzz(data []byte) int {
    cid, err := Cast(data)
    if err != nil { return 0 }
    _ = cid.Bytes()
    _ = cid.String()
    // ... exercises all methods with random input
}

Proposed Solution

1. Create tests/test_fuzz.py using hypothesis for property-based testing:

   from hypothesis import given, 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):
       """extract_prefix should raise ValueError, not crash."""
       try:
           extract_prefix(data)
       except ValueError:
           pass  # Expected
   
   @given(st.binary(max_size=100))
   def test_get_codec_never_crashes(data):
       try:
           get_codec(data)
       except ValueError:
           pass
   
   @given(st.text(max_size=100))
   def test_code_from_string_never_crashes(text):
       try:
           Code.from_string(text)
       except ValueError:
           pass
   
   @given(st.text(max_size=100))
   def test_is_codec_never_crashes(text):
       result = is_codec(text)
       assert isinstance(result, bool)

2. Add hypothesis to dev dependencies.

Related

• Dev dependency to add: hypothesis
• Test directory: tests/