olemus
(a) üldiselt:
platvorm kontseptsioonide, meetodite ja objektide uurimiseks ja korratavaks katsetamiseks
Wiktionary:
(idiomatic) any venue, setup, etc. used for experimentation, testing, proving a concept, etc.
https://en.wikipedia.org/wiki/Testbed
https://www.nist.gov/labs-major-programs/research-test-beds

(b) IT alal,
ISO/IEC/IEEE 24765:
keskkond, mis sisaldab testimiseks vajalikke riistvaravahendeid, mõõtevahendeid, simulaatoreid, tarkvarainstrumente, muid abielemente
= environment containing the hardware, instrumentation, simulators, software tools, and other support elements needed to conduct a test
https://en.wikipedia.org/wiki/LDRA_Testbed
https://arxiv.org/pdf/1610.05971.pdf