Worked on the ferdymercury/root repository to enhance the reliability of RooFormula’s substitution logic and RooConstVar handling. Focused on updating and expanding unit tests in C++ to align with new argument substitution rules, ensuring that constants used in RooFormulaVar are correctly recognized as RooConstVar, including those with numeric names. This targeted bug fix improved test coverage for edge cases, reducing the risk of regressions and supporting safer refactoring of RooFit components. The work emphasized robust software development practices and thorough unit testing, directly supporting downstream physics analyses that depend on accurate and predictable RooFormula behavior in C++ environments.