Buying property with non paying tenants.

Hello everyone, 

I'm buying a property that has tenants in it. It's hard to say whether they are still living there. There is no electric in the house but one of the tenants claims he comes back at night because he can't stand the heat during the day. 

how should I approach the situation? I don't want to close on a house with tenants. Can I evict them while I have the property under contract? What is the best way to handle the situation? I'm in Texas.