Developer Finds 140 Hidden Bugs After Porting Python String Library to Rust

A developer porting the Python string-similarity library textdistance to Rust discovered that the initial code compiled and appeared correct but contained 140 behavioral divergences from the original. To verify equivalence across more than 30 algorithms, the developer used differential fuzzing, running both the Python and Rust implementations against identical inputs and comparing outputs. Many discrepancies stemmed from subtle implementation details, including a threshold condition in the Jaro-Winkler algorithm dating back to William Winkler's 1990 paper that is routinely omitted in popular descriptions of the formula. Additional bugs arose from floating-point precision drift at the 15th decimal place, which standard unit tests were not sensitive enough to catch. The project, now published as textdistance-rs, highlights how passing an existing test suite is not sufficient proof of a correct port without deeper equivalence testing.