Fix DeepDiff in tests when OVERWRITE_TEST_EXPECTED_DATA is set

Make sure we overwrite expected test results only when there's a
meaningful diff.

tests/utilities.py

@@ -1,6 +1,7 @@
 import json
 import os
-import deepdiff
+
+from deepdiff import DeepDiff
 
 FIND_SUBJECT_VARIANTS_URL = "/subject-operations/genotype-operations/$find-subject-variants"
 FIND_SUBJECT_VARIANTS_OUTPUT_DIR = "tests/expected_outputs/find_subject_variants/"
@@ -123,12 +124,13 @@ def find_the_gene_query(query):
 
 
 def compare_actual_and_expected_output(filename, actual_json):
-    if 'OVERWRITE_TEST_EXPECTED_DATA' in os.environ:
-        with open(filename, 'w') as expected_output_file:
-            json.dump(actual_json, expected_output_file, indent=4)
-        return
-
     with open(filename) as expected_output_file:
         expected_json = json.load(expected_output_file)
-        diff = deepdiff.DeepDiff(actual_json, expected_json, ignore_order=True)
-        assert diff == {}
+        diff = DeepDiff(actual_json, expected_json, ignore_order=True)
+
+        if diff != {}:
+            if 'OVERWRITE_TEST_EXPECTED_DATA' in os.environ:
+                with open(filename, 'w') as expected_output_file:
+                    json.dump(actual_json, expected_output_file, indent=4)
+            else:
+                assert diff == {}