Testing a distributed system using a single machine may look like an unorthodox approach. From our experience, however, when building a test framework for a distributed system, everyone would be automatically led to think about building it using a single machine for many benefits, especially saving a lot time. So, I would find it very inefficient to develop a distributed system using only system tests utilizing a cluster of machines, without exploiting integration tests.

Nevertheless using just a single thread to simulate everything seems like a great approach.