def count_swaps(s):  
  zeros = 0
  ones = 0  
  for c in s:    
    if c == '0':
      zeros += 1    
      ones += 1  
  return min(zeros, ones)

t = int(input())
for _ in range(t):  
  n = int(input())  
  s = input()  
  print(count_swaps(s))