#include <bits/stdc++.h>
 #define rep(i,a,b) for (i=a;i<b;i++)
 #define rep2(i,a,b) for (i=a;i>=b;i--)
 #define mod 1000000007
 //#include<boost/multiprecision/cpp_int.hpp>
 //using namespace boost::multiprecision;
 #define FIO ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
 #define INF  1e9+5
 #define f first
 #define s second
 #define endl '\n'
 #define ll long long
 #define ii pair <int,int>
 #define pll pair <ll,ll>
 #define vi vector <int>
 #define vl vector <ll>
 #define vvi vector < vi >
 #define vii vector < ii >
 #define vvii vector < vii >
 #define vll vector < ll >
 #define vb  vector <bool>
 #define pb push_back
 #define mk make_pair
 #define sz(a) a.size()
 #define all(a) a.begin(),a.end()
 #define rall(a) a.rbegin(),a.rend()
 #define cset(a) __builtin_popcountll(a)
 #include<string>
 #include<sstream>
 using namespace std;
 int a[1000001];
 int main()
 {
    FIO;
    int t, n, m, i, top_i, x;
    ll maxx, cur_maxx;
    cin>>t;
    while(t--)
    {
        cin>>n>>m;

        memset(a,0,sizeof(a));
        rep(i,0,m)
        {
            cin>>x;
            a[x]++;
        }
        stack<int>ss;
        i = 0;
        maxx = 0;
        while(i <= n)
        {
            if( ss.empty() || a[ss.top()] <= a[i])
            {  ss.push(i);
               i++;
            }
            else
            {
                top_i = ss.top();
                ss.pop();
                if( ss.empty())
                  cur_maxx = a[top_i]*i;
                else
                  cur_maxx = a[top_i]*(i - ss.top() - 1);
                if( cur_maxx > maxx)
                 maxx = cur_maxx;
            }
        }
        while( !ss.empty())
        {
               top_i = ss.top();
                ss.pop();
                if( ss.empty())
                  cur_maxx = a[top_i]*i;
                else
                  cur_maxx = a[top_i]*(i - ss.top() - 1);
                if( cur_maxx > maxx)
                 maxx = cur_maxx;
        }
        cout<<maxx<<endl;
    }
    return 0;
 }