Strap that's testable when travelling?
I believe the answer is:
seat belt
'strap' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'testable when travelling?' is the wordplay.
'testable' anagrams to 'SEAT BELT'.
Though, I'm not clear how this is indicated.
'that's' is the link.
Can you help me to learn more?
(Other definitions for seat belt that I've seen before include "Protective device to be worn in car" , "Safety device in car - wearing mandatory" , "harness" , "Safety device worn in car" , "restraining device" .)