#include <iostream>
#include <fstream>
#include <queue>
#include <cstring>
#include <vector>
#include <cmath>
using namespace std;
ifstream fin("amici2.in");
ofstream fout("amici2.out");
#define MAX 21010
#define pb push_back
vector<int> G[MAX];
queue <int> Q;
typedef vector <int> :: iterator iter;
int viz[MAX];

int main()
{
    int t, n, m, i, x, y, nod;
    fin>>t;
    while(t--)
    {
        fin>>n>>m;
        memset(viz, 0, sizeof(viz));
        for(i=1;i<=n;i++)
            G[i].clear();
        while(m--)
        {
            fin>>x>>y;
            G[x].pb(y);
            G[y].pb(x);
        }
        Q.push(1);
        viz[1]=1;
        while(Q.size())
        {
            nod=Q.front();
            Q.pop();
            for(iter it=G[nod].begin();it!=G[nod].end();it++)
            {
                if(!viz[*it])
                {
                    viz[*it]=viz[nod]+1;
                    Q.push(*it);
                }
            }
        }
        fout<<(int)log2(2*viz[nod]-1)<<"\n";
    }
}