include port position when writing, adding test to load back compound…

… with ports

mbuild/formats/json_formats.py

@@ -158,6 +158,7 @@ def _particle_info(cmpd, include_ports=False):
             else:
                 port_info["anchor"] = None
             port_info["label"] = None
+            port_info["pos"] = port.pos.tolist()
             # Is this the most efficient way?
             for key, val in cmpd.labels.items():
                 if (val == port) and val.port_particle:
@@ -242,6 +243,8 @@ def _add_ports(compound_dict, converted_dict):
             for port in ports:
                 label_str = port["label"]
                 port_to_add = mb.Port(anchor=converted_dict[port["anchor"]])
+                if port.get("pos", None) is not None:
+                    port_to_add.translate_to(port.get("pos"))
                 converted_dict[compound["id"]].add(
                     port_to_add, label_str, check_box_size=False
                 )

mbuild/tests/test_json_formats.py

@@ -121,3 +121,12 @@ def test_float_64_position(self):
         compound_to_json(ethane, "ethane.json", include_ports=True)
         ethane_copy = compound_from_json("ethane.json")
         assert np.allclose(ethane.xyz, ethane_copy.xyz, atol=10**-6)
+
+    def test_compound_with_port(self):
+        ch2 = mb.lib.moieties.CH2()
+        ch2.save("ch2.json", show_ports=True, overwrite=True)
+
+        loaded_ch2 = mb.load("ch2.json")
+        assert len(loaded_ch2.all_ports()) == 2
+        for port in loaded_ch2.all_ports():
+            assert port.separation == 0.07