#include<iostream>
#include<stdio.h>
#include<string.h>
#include<algorithm>

using namespace std;
#define INF 0x3f3f3f3f
#define N 2000007

int s[N], S[N], p[N];

int Manacher(int len)
{
    int MaxLen = 0, index = 0, ans = 0;

    for(int i=2; i<len; i++)
    {
        if(MaxLen>i) p[i] = min(p[index*2-i], MaxLen-i);
        else p[i] = 1;

        while(s[i-p[i]]==s[i+p[i]] && (s[i-p[i]]==-2 || p[i]==1 || s[i-p[i]]<=s[i-p[i]+2]))
            p[i]++;

        if(p[i]+i>MaxLen)
        {
            MaxLen = p[i] + i;
            index = i;
        }

        ans = max(ans, p[i]);
    }
    return ans-1;
}

int main()
{
    int t;
    scanf("%d", &t);
    while(t--)
    {
        int n, i;

        scanf("%d", &n);
        s[0] = INF;
        for(i=0; i<n; i++)
        {
            scanf("%d", &S[i]);
            s[i*2+1] = -2;
            s[i*2+2] = S[i];
        }
        s[i*2+1] = -2;
        s[i*2+2] = -INF;

        printf("%d\n", Manacher(n*2+1));
    }
    return 0;
}