Set lru maxsize

Author: rmjarvis

tests/test_convolvepsf.py

@@ -21,7 +21,7 @@
 
 from piff_test_helper import timer
 
-@lru_cache
+@lru_cache(maxsize=1)
 def make_screens():
     # Some parameters copied from psf_wf_movie.py in GalSim repo.
     Ellerbroek_alts = [0.0, 2.58, 5.16, 7.73, 12.89, 15.46]  # km