Using a single thread to simulate everything is cool (as stated in my previous comment on FoundationDB at https://news.ycombinator.com/item?id=22382066). Especially if the overhead of building the test framework is small.
In our case, we use a single process to run everything, in conjunction with strong invariants written into the code. When an invariant is violated, we analyze the log to figure out the sequence of events that triggers the violation. As the execution is multi-threaded, the analysis can take a while. If the execution was single-threaded, the analysis would be much easier. In practice, the analysis is usually quick because the log tells us what is going on in each thread.
So, I guess there is a trade-off between the overhead of building the test framework and the extra effort in log analysis.
In our case, we use a single process to run everything, in conjunction with strong invariants written into the code. When an invariant is violated, we analyze the log to figure out the sequence of events that triggers the violation. As the execution is multi-threaded, the analysis can take a while. If the execution was single-threaded, the analysis would be much easier. In practice, the analysis is usually quick because the log tells us what is going on in each thread.
So, I guess there is a trade-off between the overhead of building the test framework and the extra effort in log analysis.