#include <bits/stdc++.h>
#define int long long

using namespace std;

struct DSU {
	vector <int> f;
	
	DSU (int n) {
		f.resize (n + 1);
		iota (f.begin (), f.end (), 0);
	}
	
	int find (int x) {
		return f[x] = f[x] == x ? x : find (f[x]);
	}
	
	void merge (int x, int y) {
		x = find (x);
		y = find (y);
		f[x] = y;
	}
};

void solve () {
	int n, m;
	cin >> n >> m;
	
	DSU dsu (n);
	
	for (int i = 0; i < m; i ++) {
		int x, y;
		cin >> x >> y;
		x --; y --;
		dsu.merge(x, y);
	}
	
	int sum = -1;
	for (int i = 0; i < n; i ++) {
		if (dsu.find (i) == i) {
			sum ++;
		}
	}
	
	cout << sum << '\n';
}

signed main () {
    ios::sync_with_stdio (false);
    cin.tie (nullptr);

    int T = 1;
     cin >> T;

    while (T --) {
        solve ();
    }

    return 0;
}