#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
const int inf=1e9+7;

static char buf[1000000],*p1=buf,*p2=buf;
#define getchar() p1==p2&&(p2=(p1=buf)+fread(buf,1,1000000,stdin),p1==p2)?EOF:*p1++
inline int wrd(){int x=0,f=1;char c=getchar();while(c<'0' || c>'9'){if(c=='-') f=-1;c=getchar();}while(c>='0' && c<='9') {x=(x<<3)+(x<<1)+c-48;c=getchar();}return x*f;}
inline void write(int x){static char buf[20];static int len=-1;if(x<0)putchar('-'),x=-x;do buf[++len]=x%10,x/=10;while(x);while(len>=0)putchar(buf[len--]+48);}

int n,m,k;

struct Graph{
	vector<bool> vs;
	vector<int> f,ans;
	vector<vector<int>> g;
	Graph(){
		f.resize(n+1),vs.resize(n+1),g.resize(n+1);
		for(int i=1;i<=n;++i) f[i]=i;
		ans.clear();
	}
	int fd(int x){return x==f[x]?x:f[x]=fd(f[x]);}
	void uty(int x,int y){f[fd(x)]=fd(y),g[x].push_back(y),g[y].push_back(x);}
	bool dfs(int u,int t){
		if(u==t){ans.push_back(t);return 1;}
		for(int v:g[u]){
			if(vs[v]) continue;
			vs[v]=1;
			if(dfs(v,t)){ans.push_back(u);return 1;}
		}
		return 0;
	}
};

void solve(){
	n=wrd(),m=wrd(),k=ceil(1.*m/(n-1));
	vector<Graph> G(k);
	bool flg=0;
	for(int i=1;i<=m;++i){
		int u=wrd(),v=wrd();
		int l=0,r=k-1,p=k;
		while(l<=r){
			int md=(l+r)>>1;
			if(G[md].fd(u)^G[md].fd(v)) p=md,r=md-1;
			else l=md+1;
		}
		if(p<k) G[p].uty(u,v),flg|=(p==k-1);
	}
	if(!flg){puts("-1");return;}
	int u=0,v=0;
	for(u=1;u<=n;++u) if(G[k-1].g[u].size()){v=G[k-1].g[u][0];break;}
	write(u),putchar(' '),write(v),puts("");
	for(int i=0;i<k;++i){
		G[i].dfs(v,u),write(G[i].ans.size()),putchar(' ');
		for(int x:G[i].ans) write(x),putchar(' ');
		puts("");
	}
}

signed main(){
	int T=wrd();
	while(T--) solve();
	return 0;
}