#include<bits/stdc++.h>
#define IOS ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define endl '\n'
#define fixed(s) fixed<<setprecision(12)<<s
//#define int long long
 
using namespace std;
 
typedef pair<int, int> PII;
typedef long long ll;
typedef pair<ll, PII> PLII;

const int N = 5e5 + 7;

int unit;
ll sum;
int cnt[N];

struct node {
    int l, r, mex;
    bool operator<(const node &x) const {
    if (l / unit != x.l / unit) return l < x.l;
    if ((l / unit) & 1) return r < x.r;
    return r > x.r;
    }
};

void add(int i) {
    if (cnt[i] == 0) sum++;
    cnt[i]++;
}

void del(int i) {
    cnt[i]--;
    if (cnt[i] == 0) sum--;
}

vector<int> pos[N];

void solve()
{
	int n, m;
	cin >> n >> m;
    unit = n, sum = 0;
	vector<int> a(n + 2);
	vector<int> v;
    cnt[1] = 0, cnt[m] = 0;
	for(int i = 1; i <= n; i ++)
	{
		cin >> a[i];
		v.push_back(a[i]);
		if(a[i] > 1)v.push_back(a[i] - 1);
		if(a[i] < m)v.push_back(a[i] + 1);
        cnt[a[i]] = 0;
	}
	v.push_back(1), v.push_back(m);
	
	if(n == 1 && m == 1 && a[1] == 1)
	{
		cout << -1 << endl;
		return;
	}
	for(auto x : v) pos[x].clear(), pos[x].push_back(0);
	for(int i = 1; i <= n; i ++) pos[a[i]].push_back(i);
	for(auto x : v) pos[x].push_back(n + 1);
	
    ll ans = -2e9;
    vector<node> q;
	for(auto i : v)
	{
		for(int j = 1; j < pos[i].size(); j ++)
		{
			int L = pos[i][j - 1] + 1, R = pos[i][j] - 1;
			if(L > R)continue;
			
            q.push_back({L, R, i});
		}
	}
    sort(q.begin(), q.end());
    for (int i = 0, L = 1, R = 0; i < q.size(); i++){
        while (L > q[i].l) add(a[--L]);
        while (R < q[i].r) add(a[++R]);
        while (L < q[i].l) del(a[L++]);
        while (R > q[i].r) del(a[R--]);
        ans = max(sum - q[i].mex, ans);
    }
    cout << ans << '\n';
}

int main()
{
	IOS
	int _;
	cin >> _;
	while(_ --)
	{
		solve();
	}
	
	return 0;
}