Juan Belon developed a customizable assertion handler for the curl/curl repository, enabling tailored debugging and error handling through the introduction of the CURL_DEBUGASSERT macro. By implementing this feature in C within the curl_setup_once module, Juan leveraged macro design and conditional compilation to allow developers to define custom assertion handlers suited to their specific environments. This approach enhanced the CURL library’s adaptability across development, CI, and production builds, streamlining issue diagnosis and improving portability. The work demonstrated proficiency in C programming, debugging, and library development, delivering a focused solution that addressed the need for flexible assertion handling without introducing new bugs.