I don't understand what is bad with these messages. 
I found some information about messages in assert statements in the following book:
http://www.cs.umss.edu.bo/doc/material/mat_gral_137/Addison.Wesley.Growing.Object.Oriented.Software.Guided.by.Tests.Oct.2009%20(1).pdf
But, actually, it's not helped.
Could you please provide me your point of view on this problem?