'testability' originates from English, specifically formed from the adjective 'testable' (itself from the verb 'test') plus the noun-forming suffix '-ability' (via Latin/Old French suffixes), where the root 'test-' ultimately relates to Latin 'testari' (to bear witness) and '-able/-ability' indicated 'capable of'.

'testability' developed from Middle English and Early Modern English usage of 'test' (from Old French 'tester' and Latin 'testari'), which produced the adjective 'testable' (capable of being tested), and later the nominal derivative 'testability' through the addition of the Late Latin/Old French-derived suffix '-ability'/'-abilitas'.

Initially, the root 'test-' was associated with 'witnessing' or 'bearing witness' (Latin 'testari'), but over time its usage shifted toward 'examining' or 'trying' things; the modern word 'testability' means 'the capability of being tested' rather than the older sense of witnessing.