As data rates exceed 25 Gb/s the importance of test signal fidelity grows and so does the need to characterize channels and receivers with instrument-quality equipment. If not used, waveform inadequacies either exaggerate component flaws forcing unnecessary redesigns, or they conceal flaws allowing products to ship with performance deficiencies. BERT transmitter features like multi-tap pre- and de-emphasis and multi-megabyte pattern memory are not optional at high data rates. Similarly, error detectors should synchronize quickly and stay locked even in high error environments. Read this paper to learn key test signal characteristics and necessary features for efficient development of high-quality products for 25+ Gb/s applications.