Adding back a simulation pickle test

Ensuring pickling works is needed on the backend.

Author: momchil-flex

requirements/dev.txt

@@ -11,3 +11,4 @@ pytest
 pytest-timeout
 gdspy
 memory_profiler
+dill

tests/test_IO.py

@@ -9,6 +9,7 @@
 import xarray as xr
 import h5py
 from dask.base import tokenize
+import dill as pickle
 
 
 from tidy3d import *
@@ -52,6 +53,17 @@ def test_simulation_load_export_hdf5():
     assert SIM == SIM2, "original and loaded simulations are not the same"
 
 
+@clear_tmp
+def test_simulation_load_export_pckl():
+
+    path = "tests/tmp/simulation.pckl"
+    with open(path, "wb") as pickle_file:
+        pickle.dump(SIM, pickle_file)
+    with open(path, "rb") as pickle_file:
+        SIM2 = pickle.load(pickle_file)
+    assert SIM == SIM2, "original and loaded simulations are not the same"
+
+
 @clear_tmp
 def test_simulation_preserve_types():
     """Test that all re-loaded components have the same types."""