Andreas Rohner enhanced the google/cel-go repository by developing comprehensive edge-case tests for the String.Format function. Focusing on robustness, he addressed scenarios involving negative integers in binary, octal, and hexadecimal formatting, as well as special floating-point values like NaN and infinities. Using Go and leveraging his expertise in string formatting and testing, Andreas ensured that the new tests were tightly linked to specific code changes for traceability. This work improved the reliability and maintainability of the core formatting logic, reducing the risk of regressions and supporting future refactoring efforts by providing thorough coverage of complex input cases.