From I2P(I)2017_Chen_Final_Practice
Given an undirected graph G, you have to check whether it is a bipartite graph (二分圖) or not.
The first line contains an integer T, representing the number of test cases.
For each test case:
The first line contains two integers n, m, representing the number of vertices and the number of edges.
The next m lines contain two integers u, v, representing that there is an undirected edge between vertex u and vertex v.
It is guaranteed that:
For each graph G, if G is a bipartite graph, please output "Yes", otherwise please output "No".