x = int(input())
def ck(w1,w2,m):
if w1 == w2:
return 0
res = 0
for i in range(m):
res +=abs(ord(w1[i])-ord(w2[i]))
return res
def cal(n,m,a):
ans = 26 * m
for i in range(n-1):
for j in range(i+1,n):
ans = min(ans,ck(a[i],a[j],m))
return ans
for jj in range(x):
n,m = [int(i) for i in input().split(' ')]
a = []
for i in range(n):
a.append(input())
print(cal(n,m,a))
#include<bits/stdc++.h>
using namespace std;
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
int t;
cin>>t;
for(int w=0;w<t;w++){
int n,m,i,j,min=0,k,a=0;
cin >> n >> m;
vector < string > v(n);
for(i=0;i<n;i++){
cin >> v[i];
}
for(i=0;i<m;i++){
min=min+abs((v[0])[i]-(v[1])[i]);
}
for(i=0;i<n;i++){
for(j=i+1;j<n;j++){
for(k=0;k<m;k++){
a=a+abs((v[i])[k]-(v[j])[k]);
}
if(a<min){
min=a;
}
a=0;
}
}
cout << min << endl;
}
}
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