The famous philosopher Socrates was brought to trial in Athens in 399 BC, charged with the corruption of youth and with impiety. His accusers likely held personal and political grudges against Socrates more than anything else, yet they testified against him before five hundred Athenian jurors. Socrates spoke on his own behalf, but he refused to call any witnesses to support his testimony or to defend him. He even refused to call in his wife and children, as was common. The jury convicted Socrates 280 to 220 and then chose to subject Socrates to the death penalty. Socrates was executed about a month later by hemlock poisoning.
The question, then, is whether or not Aristotle would see Socrates' decision not to call supporting witnesses as virtuous. For Aristotle, virtue is the mean between the extremes of excess (too much) and deficiency (too little). For instance, the virtue of modesty is the mean between the excess of shyness (being so modest that one cannot even interact with others) and the deficiency of shamelessness (being so immodest that one has no shame and presents oneself to others in a brazen and depraved manner).
Aristotle would probably say that Socrates was violating the virtues or mean of temperance and proper ambition or pride by failing to call witnesses. Socrates cared so little about himself and whether he lived or died that he failed in temperance and fell into the deficiency of insensibility. He spoke in his own defense but failed to receive the help of others, whose testimony might have saved him from death. Also, Socrates' nonchalant lack of self-preservation might be viewed by Aristotle as a deficiency of proper ambition or pride. Socrates fell into the deficiency of “un-ambition,” again not caring whether he lived or died. As a mean, Aristotle might recommend that Socrates both defend himself against the charges and call a few of his friends and students as witnesses to support his claims and dispute his opponents. This, Aristotle would likely say, would be much more a middle ground of responsible self-preservation and much more virtuous.