Reader Ram asks:

“… should an SDET be an SME in the application or be an SME in automation only or should be an SME is both application under test and automation tool? “

Full comment is here.

A tester can do many things, but very few can do everything. It’s ok to specialize either in the product, or an aspect of testing such as security or performance. When some colleagues and I created the Microsoft tester personas, one of the things we wanted to highlight was that an experienced testers role may be that of a subject matter expert, or in a variety of other roles. Jodi is a fantastic tester (and product SME), but Sanjay, Alecha and Kazutoshi are all fantastic testers too. It’s really up to the individual tester and the organization to allow testers to contribute their strengths to the entire testing effort.