#include <bits/stdc++.h>
#define il inline
#define ll long long
#define int ll
#define Max 500005
using namespace std;
il ll read()
{
	char c=getchar();
	ll x=0,f=1;
	while(c>'9'||c<'0')
	{
		if(c=='-') f=-1;
		c=getchar();
	}
	while(c>='0'&&c<='9')
	{
		x=x*10+c-'0';
		c=getchar();
	}
	return x*f;
}
#define lowbit(x) x&-x
int n,m,a[Max];
int t[Max];
void ins(int x,int k)
{
	for(int i=x;i<=n;i+=lowbit(i)) t[i]+=k;
}
int query(int x)
{
	int res=0;
	for(int i=x;i;i-=lowbit(i)) res+=t[i];
	return res;
}
signed main()
{
	int T=read();
	while(T--)
	{
		n=read(),m=read();
		vector<vector<int>> p(n+1); 
		for(int i=1;i<=n;i++) 
		{
			t[i]=0;
			a[i]=read();
			if(a[i]<=n) p[a[i]].push_back(i);
		}
		vector<array<int,3>> qry;
		int tot=0;
		for(int i=1;i<=n;i++)
		{
			if(!p[i].size()) continue;
			int l=1;
			for(auto r:p[i])
			{
				if(l<r) qry.push_back({r-1,l,tot++});
				l=r+1;
			}
			if(l<=n) qry.push_back({n,l,tot++});
		}
		sort(qry.begin(),qry.end());
		vector<int> vst(n+1,0);
		vector<array<int,2>> ans;
		int nw=0;
		for(int i=1;i<=n;i++)
		{
			if(vst[a[i]])
			{
				ins(vst[a[i]],-1);
			}
			ins(i,1);vst[a[i]]=i;
			while(nw<qry.size()&&qry[nw][0]==i)
			{
				int l=qry[nw][1],r=qry[nw][0];
				ans.push_back({qry[nw][2],query(r)-query(l-1)});
			//	cout<<l<<' '<<r<<' '<<query(r)-query(l-1)<<" qwq\n";
				nw++;
			}
		}
		sort(ans.begin(),ans.end());
		tot=0;
		int res=-1;
		for(int i=1;i<=n;i++)
		{
			if(!p[i].size()) continue;
			int l=1;
			for(auto r:p[i])
			{
				if(l<r) res=max(res,ans[tot++][1]-i);
				l=r+1;
			}
			if(l<=n) res=max(res,ans[tot++][1]-i);
		}
		cout<<res<<"\n";
	}
}