It was interesting to read all the opinions. I can understand both, man and woman, and don't see why one of them has to be condemned. People go the courts for justice and they get a verdict. In some situations, there is no way that hurts nobody.
As a reaction, the German minister of justice has said she will ask the parliament to pass a law that will make it easier for men than it still is to legally question the paternity. On the other side, surrepetitious tests should be punished harsher.
I think the old idea that each child has been fathered by the husband as long as it is conceived during a marriage. Pater semper incertus was a pre-DNA idea that has led to lawmaking that is not really appropriate for much longer. Paternity could be tested routinely at birth for instance.
The idea to stop paying does not work in Germany BTW. The money for the kid is usually taken directly from your salary before you see it, so you just have no chance not to pay.
That such cases come up is due (beside DNA developments) to a (one or two decades old) move by the German legislator to treat out-of-wedlock children just like "legitimate" children. Out-of-wedlock children now have the right to inherit from a biological father they may not have seen all their lives.
That has led to another case BTW: A (out-of-wedlock) daughter suing her mother to tell her the biological father(s). Mother say no, that's private and noone else's business. Dauther say her mother is preventing her rights to inherit from the biological father.