Building a complex system requires writing and debugging many tests. Developer tests that can be run without any infrastructure or configuration are crucial for allowing fast-paced development while avoiding regressions. Even for a distributed system like CockroachDB, tests that run on a single anode (e.g. as part of go test) can cover many aspects of the system: one technique we use is that of creating a virtual test cluster with multiple CockroachDB nodes, all running within the same process.