python310Packages.accupy: fix darwin build

pkgs/development/python-modules/accupy/default.nix

@@ -1,4 +1,5 @@
 { lib
+, stdenv
 , buildPythonPackage
 , fetchFromGitHub
 , pythonOlder
@@ -56,6 +57,10 @@ buildPythonPackage rec {
     export HOME=$(mktemp -d)
   '';
 
+  # This variable is needed to suppress the "Trace/BPT trap: 5" error in Darwin's checkPhase.
+  # Not sure of the details, but we can avoid it by changing the matplotlib backend during testing.
+  env.MPLBACKEND = lib.optionalString stdenv.isDarwin "Agg";
+
   # performance tests aren't useful to us and disabling them allows us to
   # decouple ourselves from an unnecessary build dep
   preCheck = ''