There are two obvious mistakes. Firstly you can't access radio groups by index. You need to use getElementsByName('testa') to get a collection of the relevant group and then loop through this collection as you have done:
var colGroup = getElementsByName('testa');
for (var i = 0; i < colGroup.length; i++)
if (colGroup.checked) return true;
The second error is that your function will always return after testing the first group. You need to change it so that it returns false if it fails but if it succeeds then does the second check against the other group.
Joe (Microsoft MVP - XML