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

const int N = 2e5+5;
int n, m, dis1[N], dis2[N];
bool vis[N];
vector<int> G[N], nG[N];

void dfs1(int x) {
    vis[x] = true;
    for (auto v : G[x]) {
        if (vis[v]) continue;
        nG[x].push_back(v);
        nG[v].push_back(x);
        dfs1(v); 
    }
}

int dfs2(int x, int f, int dis[]) {
    int res = x;
    for (auto v : nG[x]) {
        if (v==f) continue;
        dis[v] = dis[x] + 1;
        int tmp = dfs2(v, x, dis);
        if (dis[tmp] > dis[res]) res = tmp;
    }
    return res;
}

void solve() {
    cin >> n >> m;
    for (int i=1; i<=n; ++i) G[i].clear(), nG[i].clear(), vis[i]=false, dis1[i]=dis2[i]=-1;
    for (int i=1; i<=m; ++i) {
        int u, v; cin >> u >> v;
        G[u].push_back(v); G[v].push_back(u);
    }
    dfs1(1);
    // puts("111111");
    dis1[1] = 0; int x = dfs2(1, -1, dis1); 
    dis1[x] = 0; int y = dfs2(x, -1, dis1);
    dis2[y] = 0; dfs2(y, -1, dis2);
    // printf("x=%d y=%d\n", x, y);
    // printf("dis1:"); for (int i=1; i<=n; ++i) printf("%d ", dis1[i]); puts("");
    // printf("dis2:"); for (int i=1; i<=n; ++i) printf("%d ", dis2[i]); puts("");

    int sqr = (int)sqrtl(n);
    // printf("sqr=%d\n", sqr);
    if (sqr*sqr < n) ++sqr;

    vector<int> ans;
    for (int i=1; i<=n; ++i) {
        if (dis1[i]+dis2[i]==dis1[y] && dis1[i]%sqr==0) ans.push_back(i);
    }

    cout << ans.size() << '\n';
    for (int x : ans) cout << x << ' '; cout << '\n';
}

signed main() {
    ios::sync_with_stdio(0); cin.tie(0);
    int t; cin >> t; while (t--) solve();
    return 0;
}