The process of gene expression involves DNA transcription into mRNA and translation of mRNA into protein.
During transcription, genetic message in DNA is encoded into mRNA. The encoded messages are then translated into their respective amino acids during the process of translation.
<em>Hence, if a virus uses its genome as mRNA, the next stage will be to translate the messages in the mRNA into amino acids. Translation rate is expected to be measurable.</em>
He could race multiple cars with different weight added on them and do multiple races (just to be sure) and see if his theory was correct, if not he should right down what he has learned from his experience! :D