Why is it "ihr euch" and not just "euch", does it have to do something with how the verb is inflected?

Why is it “ihr euch” and not just “euch”, does it have to do something with how the verb is inflected?

The infinitive is “sich testen”. Like with any other reflexive verb that requires the accusative case “sich” changes as follows:
ich teste mich
du testest dich
er/sie/es testet sich
wir testen uns
ihr testet euch
sie testen sich

Please have a look at this recent post:

uns - If Wir is “we” and uns is “us”, why do they go together? “We us not” doesn’t make sense, right?