#include<cstdio>

#include<cstring>

#include<cstdlib>

#include<algorithm>

using namespace std;

struct LSnode

{

    int x,p,z;

}A[],B[];

int cmp(const void *x1,const void *x2)

{

    LSnode n1=*(LSnode *)x1;

    LSnode n2=*(LSnode *)x2;

    return n1.x-n2.x;

}

int s[];

int id[];

int back[];

int main()

{

    int t;

    scanf("%d",&t);

    while(t--)

    {

        int n;

        scanf("%d",&n);

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

        {

            scanf("%d",&A[i].x);

            A[i].p=i;

        }

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

        {

            B[i].x=A[i].x;

            B[i].p=A[i].p;

        }

        qsort(B+,n,sizeof(LSnode),cmp);

        B[].z=;

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

        {

            if(B[i].x==B[i-].x) B[i].z=B[i-].z;

            else B[i].z=B[i-].z+;

        }

        int zz=;

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

        {

            A[B[i].p].z=B[i].z;

            zz=max(zz,B[i].z);

        }

        for(int i=;i<=n;i++) back[A[i].z]=A[i].x;

        memset(s,,sizeof(s));

        int mmax=;

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

        {

            s[A[i].z]++;

            mmax=max(mmax,s[A[i].z]);

        }

        int len=;

        for(int i=;i<=zz;i++) if(s[i]==mmax) id[++len]=back[i];

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

        else

        {

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

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

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

        }

    }

    return ;

}