for i in range(int(input())):
    n=int(input())
    s=input()
    count=0
    odd=0
    x=0
    y=0
    for j in range(n):
        if s[j]=='0':
            count +=1
        if s[j]=='1':
            odd+=1
    for z in range(count):
        if s[z]=='1':
            x+=1
    for k in range(odd):
        if s[k]=='0':
            y+=1
    if x>y:
        print(y)
    if y>x:
        print(x)
    if x==y:
        print(x)