Thank you for your response corporate-wage-slave . I didn't know that about Hungary changing its regulations a lot.

I just received a reply from Vienna airport confirming that they won't require a test from me, unless I want to exit the airport(same is true for all transits if anyone is interested). The layover though is 13 hr instead of 6 hr in London so I will wait to hear from them as well. Could you tell me where you got your info or it it just an assumption based on the low cases of covid in both countries?