#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;

#define forr(_a, _b, _c) for(_a = (_b); _a <= (_c); ++_a)
#define ford(_a, _b, _c) for(_a = (_b) + 1; _a --> (_c);)
#define forf(_a, _b, _c) for(_a = (_b); _a < (_c); ++_a)
#define mp make_pair
#define fi first
#define se second
#define vi vector
#define sz(_v) _v.begin(), _v.end()
#define mask(_x) (1ll << (_x))
#define bit(_x,_y) (((_x) >> (_y)) & 1)

string yes[2] = {"NO\n","YES\n"};
const ld eps = ld(1e-7);
const ll inf = ll(1e16) + 1;
const ll mod = ll(1e9) + 7;

const int N = 2e5 + 5;
int n, i, a[N], ma;

void solve() {
	cin >> n;
	ma = 0;
	forr(i,1,n) {
		cin >> a[i];
		ma = max(ma,a[i]);
	}
	sort(a + 1,a + 1 + n);
	forr(i,1,n) {
		if(a[i] == ma) {
			if(n - i > 1) {
				cout << "-1\n";
			} else {
				cout << i << "\n";
			}
		}
	}
}

void precalc() {
}

int main() {
	ios_base::sync_with_stdio(false); cin.tie(NULL);
	#ifdef umf
		freopen("test.inp","r",stdin);
		freopen("test.out","w",stdout);
	#endif

	int tc = 1;
	cin >> tc;
	precalc();
	while(tc --> 0) {
		solve();
	}

	return 0;
}