Speak or Announce
Text isn't important. Read the side of a milk carton or back of a cereal box, but do it in your normal presenting/announcing style.
Read longer than about 15 seconds and use many different words. "Testing one two one two one two" for 15 seconds isn't useful.
Your voice should peak occasionally around the yellow region (-6dB to -10dB) of the Audacity gradient sound meters.
Many people are shocked to discover they are expected to watch the sound meters and read copy at the same time. You are replacing the sound engineer who would normally be watching the meters for you.