Where does “tester” come from?

tester (French) comes from French test, from English Test, from German testen, from German Test, from English test, from Middle English teste, from Old French teste, from Latin testis — to stand.

tester (French): to test; to write one's will

Definitions

to test; to write one's will

Ancestry of “tester”, step by step

tester traces back through two separate lines of ancestry.

via French test

Step	Language	Word	Meaning
1	French	test	test, a cupel or cupelling hearth in which...
2	English	Test	a Test match
3	German	testen	to test
4	German	Test	test; melting pot
5	English	test	A challenge, trial; A cupel or cupelling hearth...
6	Middle English	teste	—
7	Old French	teste	head
8	Latin	testis	witness; one who testifies or attests; testicle
9	Latin	terstis	—
10	Latin	trīstis	sad, unhappy, melancholy, morose
11	Proto-Indo-European	tristh₂s	a third party standing, after the two parties to...
12	Proto-Indo-European	steh₂-	to stand

via Latin testor

Step	Language	Word	Meaning
1	Latin	testor	I am witness, testify, attest; I make a will
2	Latin	-ō	suffixed to nouns or adjectives. Originally a-stem nouns. Later extended to nouns with other stems. Forms regular first-conjugation verbs
3	Proto-Indo-European	-ō	Derives nouns from roots

Words derived from “tester”

Every word from Proto-Indo-European steh₂- →Every word from Proto-Indo-European tristh₂s →Every word from Latin trīstis →