summer_battle_C

#include <iostream>

#include <vector>
#include <hash_map>
#include <algorithm>
#include <utility>
#include <queue>
#include <functional>
using namespace std;

int main()
{
	int n;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		int n,m,s,e;
		cin >> n >> m >> s >> e;
		vector<pair <int, int > > v;
		for (int j = 0; j < m; j++)
		{
			int p, q;
			cin >> p >> q;
			v.push_back({ p, q });
		}
		queue <int > qu, pu;
		vector <bool> matrix(n+1, false);
		int d = 0;
		qu.push(s);
		while (qu.size() || pu.size())
		{
			int now = qu.front();
			if (!matrix[now] )
			{
				matrix[now] = true;
				if (now == e)
					break;
				for (pair <int, int> arg : v)
				{
					if (arg.first == now && !matrix[arg.second])
						pu.push(arg.second);
				}
			}
			qu.pop();
			if (qu.empty() && pu.size())
			{
				qu = pu;
				while (pu.size()) pu.pop();
				d++;
			}
		}
		if (matrix[e])
			cout << d << endl;
		else
			cout << "-1" << endl;
	}
}