q=int(input().strip())
for query in range(0,q):
    n=int(input().strip())
    count=0
    sum=0
    for points in range(0,n):
        x,y=[int(arr_temp) for arr_temp in input().strip().split()]
        if(x==0 and y==0):
            count+=1
        elif(x==0 and y!=0):
            if(sum==0):
                sum=y
                count+=1
            else:
                if(sum==y):
                    count+=1
        elif(y==0 and x!=0):
            if(sum==0):
                sum=x
                count+=1
            else:
                if(sum==x):
                    count+=1
        elif(x==y):
            if(sum==0):
                sum=x
                count+=1
            
            else:
                if(sum==x):
                    count+=1
        
    if(count==n):
        print("YES")
    else:
        print("NO")