#include<cstdio>

 #include<cstring>

 #include<cstdlib>

 #include<cmath>

 #include<algorithm>

 using namespace std;

 int T;

 struct node

 {

     int x,y,id;

 }a[],b[];int s[],ans[],A[];

 bool v[];

 bool cmp(node n1,node n2){return n1.x<n2.x;}

 int main()

 {

     scanf("%d",&T);

     while(T--)

     {

         int n,m=;scanf("%d",&n);

         for(int i=;i<=n;i++)scanf("%d",&a[i].x),a[i].y=i;

         for(int i=;i<=n;i++)b[i]=a[i];

         sort(b+,b+n+,cmp);

         b[].id=;

         for(int i=;i<=n;i++)

         {

             if(b[i].x!=b[i-].x)b[i].id=b[i-].id+;

             else b[i].id=b[i-].id;

         }

         for(int i=;i<=n;i++)a[b[i].y].id=b[i].id,m=max(m,b[i].id);

         for(int i=;i<=n;i++)ans[a[i].id]=a[i].x;memset(s,,sizeof(s));

         int maxx=;for(int i=;i<=n;i++)s[a[i].id]++,maxx=max(s[a[i].id],maxx);int len=;

         for(int i=;i<=m;i++)if(s[i]==maxx)A[++len]=ans[i];

         if(len==m)printf("-1\n");

         else

         {

             printf("%d\n",len);

             for(int i=;i<len;i++)printf("%d ",A[i]);

             printf("%d\n",A[len]);

         }

     }

     return ;

 }