The NestedFunctionExecutionDistributedTest uses OperationExecutors MAX_FE_THREADS to configure both client function invocations and cache server max connections.
It uses MAX_FE_THREADS * 2 for function executions which use Function Execution Processor threads:
And potentially MAX_FE_THREADS * 3 for client connections which use ServerConnection threads:
MAX_FE_THREADS was changed recently to:
It doesn't need to use this many threads to test the behavior it is testing.