Marie caressait son chat / Son chat était caressé par Marie

Question

In English - Marie was stroking her cat / Her cat was being stroked by Marie   - but était caressé is 'was stroked' or 'used to be stroked' - am I right?

Maarten Kamp · Accepted Answer

Chris,
in the passive voice ‘ être ‘ is an auxiliary verb that conveys the tense of the principal verb in the passive voice structure, which will be the same tense as that verb is/ would be in the active voice sentence. 
As the active voice verb caresser in the sentence is in imparfait  ‘ caressait ‘, the passive voice requires être in imparfait followed by the past participle of the verb caresser. The past participle is conjugated in agreement with the passive voice subject -  the cat.   
Hence the passive voice form of the verb is ‘ était caressé ‘.  The translation as  .. ‘ was being stroked by .. ‘  is correct. 
Think about it in English - ( As/when/while ) Marie was stroking the cat, the cat was being stroked by Marie. 
https://progress.lawlessfrench.com/revision/glossary/voice/la-voix-passive-passive-voice
 
https://www.lawlessfrench.com/grammar/passive-voice-conjugations/