Blockchain, like any other complex technology, needs a strong testing methodology to support its evolution in both research and development contexts. Setting up meaningful tests for permissionless blockchain technology is a notoriously complex task for several reasons: software is complex, large number of nodes are involved, network is non ideal, etc. Developers usually adopt small virtual laboratories or costly real devnets, based on real software. Researchers usually prefer simulations of a large number of nodes, based on simplified models. In this paper, we aim to obtain the advantages of both approaches, i.e., performing large, realistic, inexpensive, and flexible experiments, using real blockchain software within a virtual environment. To do that, we tackle the challenge of running large blockchain networks in a single physical machine, leveraging Linux and Docker. We analyze a number of problems that arise when large blockchain networks are emulated and we provide technical solutions for all of them. Finally, we describe two experiences of emulating fairly large blockchain networks on a single machine, adopting both research oriented and production oriented software, and involving up to more than 3000 containers.