New capabilities in the Tessent® TestKompress® and the Tessent FastScan™ tools enable higher defect coverage and lower defect per million levels. User-defined fault models (UDFM) and a cell-aware ATPG flow combine to target subtle shorts and opens internal to standard cells not adequately detected with the standard stuck-at or transition fault models. A one-time cell library characterization flow uses Calibre® extraction tools and the Eldo® product for transistor-level fault simulation. Cell internal fault models are automatically incorporated into TestKompress pattern generation using the UDFM syntax.