Use unified_diff

pre_commit_hooks/pretty_format_json.py

@@ -59,7 +59,7 @@ def parse_topkeys(s):  # type: (str) -> List[str]
 def get_diff(source, target):  # type: (str, str) -> str
     source_lines = source.splitlines(True)
     target_lines = target.splitlines(True)
-    diff = ''.join(difflib.ndiff(source_lines, target_lines))
+    diff = ''.join(difflib.unified_diff(source_lines, target_lines))
     return diff
 
 

tests/pretty_format_json_test.py

@@ -111,22 +111,24 @@ def test_diffing_output(capsys):
     resource_path = get_resource_path('not_pretty_formatted_json.json')
     expected_retval = 1
     expected_out = '''\
-  {
+---
--     "foo":
++++
--     "bar",
+@@ -1,6 +1,9 @@
--         "alist": [2, 34, 234],
+ {
-+   "alist": [
+-    "foo":
-+     2,
+-    "bar",
-+     34,
+-        "alist": [2, 34, 234],
-+     234
+-  "blah": null
-+   ],
++  "alist": [
--   "blah": null
++    2,
-+   "blah": null,
++    34,
-?               +
++    234
-+   "foo": "bar"
++  ],
-  }
++  "blah": null,
++  "foo": "bar"
+ }
 
-'''
+'''  # noqa: W291
     expected_err = 'File {} is not pretty-formatted\n'.format(resource_path)
 
     actual_retval = main([resource_path])