#include <bits/stdc++.h>  
using namespace std;  

#define int long long  

constexpr int mod = 1e9 + 7;

void solve() {
	int n;
	cin >> n;

	vector<int> a(n + 1);
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
	}

	if (a[1] != 0 || a[n] != n - 1) {
		cout << 0 << "\n";
		return;
	}
	for (int i = 2; i <= n; i++) {
		if (a[i] < a[i - 1]) {
			cout << -1 << "\n";
		}
		if (a[i] + 1 < i) {
			cout << 0 << "\n";
			return;
		}
	}

	int ans = 1;
	for (int i = 2; i <= n; i++) {
		if (a[i] != a[i - 1]) {
			ans = ans * 2 % mod;
		} else {
			ans = ans * (a[i] + 1 - (i - 1)) % mod;
		}
	}
	cout << ans << "\n";
}

signed main() {  
    ios::sync_with_stdio(false);
    cin.tie(nullptr);  

    int t;
    cin >> t;
    while (t--) {
    	solve();
    }

    return 0;
}