// @author godmar
// slow I/O
import java.util.*;

public class onlyoneorder_godmar
{
    @SuppressWarnings("unchecked")
    static int doOne(Scanner sc) {
        int n = sc.nextInt();
        int m = sc.nextInt();
        int []p = new int[n-1];
        
        boolean bad = false;
        for (int i = 0; i < m; i++) {
            int a = sc.nextInt() - 1;
            int b = sc.nextInt() - 1;
            if (a > b)
                bad = true;
            if (a + 1 == b)
                p[a] = 1;
        }
        return bad ? -1 : n - 1 - Arrays.stream(p).sum();
    }

    public static void main(String []av) {
        var sc = new Scanner(System.in);
        int T = sc.nextInt();
        for (int i = 0; i < T; i++)
            System.out.println(doOne(sc));
    }
}