ReadySet is independent practice — not the official test. For the real thing, here are the actual bodies that run each program: NAPLAN's government and curriculum authorities plus every state and territory education department, and ICAS Assessments' own subject and FAQ pages.
Each state/territory education body's own NAPLAN page — key dates, exemptions, and how results are reported locally.
ICAS is a voluntary international academic competition run by ICAS Assessments — a separate program from NAPLAN, not a government test.
Each subject's own official page. ReadySet currently offers practice for the 4 marked available in ReadySet below.