Fix test cases for unified_diff

Author: joepin

tests/pretty_format_json_test.py

@@ -111,9 +111,7 @@ def test_diffing_output(capsys):
     resource_path = get_resource_path('not_pretty_formatted_json.json')
     expected_retval = 1
     expected_out = '''\
----
-+++
-@@ -1,6 +1,9 @@
+--- \n+++ \n@@ -1,6 +1,9 @@
  {
 -    "foo":
 -    "bar",
@@ -128,7 +126,7 @@ def test_diffing_output(capsys):
 +  "foo": "bar"
  }
 
-'''  # noqa: W291
+'''
     expected_err = 'File {} is not pretty-formatted\n'.format(resource_path)
 
     actual_retval = main([resource_path])