Add custom JSON encoder to handle attachment objects

tests/utils/test_json.py

@@ -0,0 +1,15 @@
+import json
+from atst.utils.json import CustomJSONEncoder
+
+from tests.factories import AttachmentFactory
+
+
+encoder = CustomJSONEncoder()
+
+
+def test_custom_encoder_serializes_attachments():
+    filename = "jar_jar_is_secretly_a_sith_lord.pdf"
+    attachment = AttachmentFactory.create(filename=filename)
+    encoded = encoder.encode({"file": attachment})
+    expected = json.dumps({"file": filename})
+    assert encoded == expected