In combined electric and heat systems, selecting a suitable testbed for power flow analysis or economic dispatch is not easy: a large number of existing testbeds are not open-source, while others are difficult to be reused by other researchers due to the particularity of system scale, topology, and data. In this paper, we present three open-source testbeds with different scales based on practical combined electric and heat systems. To satisfy researchers' specific demands on the system topology and data, we also discuss how to modify testbeds based on existing topologies and data. Researchers can use the testbeds presented in this paper to test their innovative methods for power flow analysis and economic dispatch, and can also design their own testbeds based on the methodology in this paper, using published topologies and data.