#include <bits/stdc++.h>

using namespace std;

const int MAX = 21001;

int best;
vector < int > myVector[MAX];
bitset < MAX > beenThere;
queue < int > myQueue;
int D[MAX];
int T,N,M;

inline void Read()
{
    scanf("%d%d", &N , &M);

    for ( int i = 1; i <= M ; ++i)
    {
        int x,y;
        scanf("%d%d", &x , &y);

        myVector[x].push_back(y);
        myVector[y].push_back(x);
    }
}

inline int BFS(int currentNode)
{
    myQueue.push(currentNode);
    beenThere[currentNode] = true;
    best = 0;

    while(!myQueue.empty())
    {
        int node = myQueue.front();
        myQueue.pop();

        for ( auto &neighbor : myVector[node])
        {
            //int neighbor = myVector[node][k];
            if(!beenThere[neighbor])
            {
                myQueue.push(neighbor);
                beenThere[neighbor] = true;
                D[neighbor] = D[node]+1;
                best = D[neighbor];

            }
        }
    }
    return best;
}

int main()
{
    freopen("amici2.in" , "r" , stdin);
   freopen("amici2.out" , "w" ,stdout);

     scanf("%d", &T);

    for ( int i = 1 ; i <= T ; ++i)
    {
       for ( int j = 1; j <= N ; ++j)
            myVector[j].clear();

            beenThere.reset();
            Read();
        int Answer = ceil(log2(BFS(1)));


        printf("%d\n" , Answer);

    }
}