#include <iostream>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <vector>
#include <map>
#include <unordered_map>

const int N = 1e5 + 10;
const int M = 2e5 + 10;
int t, n, m, k, ansu, ansv, dep[N];
std::unordered_map < int, int > fa[N];
std::unordered_map < int, std::vector < int > > f[N];

int Find (int x, int id) {
	if (fa[id][x] == x) return x;
	fa[id][x] = Find (fa[id][x], id);
	return fa[id][x];
}

bool check (int a, int b, int id) {
	a = Find (a, id), b = Find (b, id);
	return a == b;
}

void merge (int a, int b, int id) {
	a = Find (a, id); b = Find (b, id);
	if (a == b) return ;
	fa[id][a] = b;
}

void dfs (int x, int father, int id) {
	fa[id][x] = father;
	dep[x] = dep[father] + 1;
	for (auto to : f[id][x]) {
		if (to == father) continue;
		dfs (to, x, id);
	}
}

void Main () {
	std::cin >> n >> m;
	k = std::ceil(double(m) / double(n - 1));
	for (int i = 1; i <= k; i++)
		for (int j = 0; j <= n; j++)
			fa[i][j] = j;
	for (int i = 1, u, v; i <= m; i++) {
		std::cin >> u >> v;
		int l = 1, r = k + 1;
		while (l < r) {
			int mid = (l + r) >> 1;
			if (check(u, v, mid)) l = mid + 1;
			else r = mid; 
		}
		if (l <= k) {
			merge(u, v, l);
			f[l][u].push_back(v);
			f[l][v].push_back(u); 
		}
	}
	ansu = ansv = -1;
	for (int i = 1; i <= n; i++) 
		if (fa[k][i] != i) {
			ansu = i, ansv = fa[k][i];
			break;
		}
	if (ansu == -1) {
		printf("%d\n", ansu);
	} else {
		printf("%d %d\n", ansu, ansv);	
		for (int i = 1; i <= k; i++) {
			dep[ansv] = 0;
			dfs (ansv, 0, i);
			printf("%d ", dep[ansu]);
			for (int now = ansu; now != ansv; now = fa[i][now])
				printf("%d ", now);
			printf("%d\n", ansv); 
		}
	}
	for (int i = 1; i <= k; i++)
		fa[i].clear(), f[i].clear();
}

int main() {
	std::cin >> t;
	while (t--) Main();
	return 0;
}