I would like to limit the number of processes used by the MPICH Test Suite, which I run by "make testing" after building MPICH. I tried export MPITEST_PPNMAX=<n> # The maximum number of processes per node. but this had no apparent effect: some tests still ran using more than 4 processes, when I replaced <n> by 4. How could I restrict these tests to run with maximum 4 processes, for example?