Preliminary test blueprints from Smarter Balanced for ELA and math summative assessments. There's a lot to explore here: rubrics, test blueprints, etc. Read the appendices for examples of text used for assessment: the Dalai Lama and Marcus Aurelius, not insulation manuals!
This rubric from the DOE of New York City can be used by teachers and library staff to determine text complexity. With modification, it would also be useful for students to help them choose books in the library for research projects.