Develop and execute unit, I/O, integration, FAT/SAT, communications, failure-mode, alarm/interlock, performance, and regression testing; commission systems in the field and perform root-cause troubleshooting across hardware, software, networking, and instrumentation. Create and maintain functional and software design specifications, architectures, I/O lists, PLC/HMI documentation, interface-control documents, test and commissioning procedures, troubleshooting guides, release notes, and as-built records through formal engineering change control.