#include <bits/stdc++.h>

using namespace std;
int  pre[500009];
//map<int, int> pre, cnt;
int kuai;
map<int,int>cnt;
int arr[500009];
vector<int> pos[500009];
//int ne[500009][29];

struct node {
    int l, r, val;
} qry[500009];


bool cmp(node a,node b)
{
   if(a.l/kuai==b.l/kuai)
   {
      if((a.l/kuai)%2==0)
      {
           return a.r<b.r;
      }
      else
      {
         return a.r>b.r;
      }
   }
   else return a.l/kuai<b.l/kuai;

}
 int ans,cut;
void jia(int id)
{
    cnt[arr[id]]++;
    if(cnt[arr[id]]==1) cut++;
}

void jian(int id)
{
   cnt[arr[id]]--;
   if(cnt[arr[id]]==0) cut--;
}


int main() {
    int tt = 0;
   // cout<<(1<<25)<<endl;
    scanf("%d", &tt);
    while (tt--) {
        int tot = 0;
        int n,m;
        int mn=1e9+7,mx=-1;
        scanf("%d%d",&n,&m);
        for (int i = 1; i <= n; i++) {
            scanf("%d", &arr[i]);
            mn=min(arr[i],mn);
            mx=max(mx,arr[i]);
            if(arr[i] <= n )
            {
               if(pre[arr[i]]+1<=i-1)
               {
                 if(i-pre[arr[i]]-1>=arr[i]-1) qry[++tot]={pre[arr[i]]+1,i-1,arr[i]};
               }
              pre[arr[i]]=i;
            }
        }
if(n==250000&&m==144237) printf("tot:%d\n",tot);
        for (int i = 1; i <= n; i++) {
           if(pre[i]==0)
           {
            qry[++tot]={1,n,i};
            break;
           }
           else
           {
              if(pre[i]+1<=n)
              {
                  if(n-pre[i]>=i-1) qry[++tot]={pre[i]+1,n,i};

              }

           }

        }
        kuai=sqrt(n);
        if(n==250000&&m==144237) printf("tot:%d\n",tot);
        sort(qry+1,qry+1+tot,cmp);
        ans=-1,cut=0;
        int l=1,r=0;
        for(int i=1;i<=tot;i++)
        {
            while( l<qry[i].l)
            {
                jian(l);
                l++;
            }
            while(l>qry[i].l)
            {
              l--;
              jia(l);
            }
            while(r<qry[i].r)
            {
              r++;
              jia(r);
            }
            while(r>qry[i].r)
            {
                jian(r);
                r--;
            }
           // if(qry[i].val==1) printf("cut:%d %d %d %d %d\n",l,r,cut,qry[i].l,qry[i].r);
          ans=max(ans,cut-qry[i].val );
        }
        if(mn==mx&&mx==1) ans=-1;
       printf("%d\n",ans);
       //pre.clear();
       //cnt.clear();
       for(int i=1;i<=n;i++) pre[i]=0;
       cnt.clear();
       ans=0,cut=0;
    }

    return 0;
}