.thenReturn(Mono.just(existingMessage));
// Needed for readable error-reports, in case of a bug that leads to according unwanted call
when(chatRoomService.persistMessage(any(Message.MessageKey.class), any(LocalDateTime.class), any(String.class)))
.thenReturn(Mono.just(existingMessage));
// Needed for readable error-reports, in case of a bug that leads to according unwanted call
when(chatRoomService.persistMessage(any(Message.MessageKey.class), any(LocalDateTime.class), any(String.class)))