Remove extra cli flag, and update test case

This commit uses capsys to test the output of the diff, which is now
hidden behind the autofix flag if it's disabled

pre_commit_hooks/pretty_format_json.py

@@ -56,12 +56,12 @@ def parse_topkeys(s):  # type: (str) -> List[str]
     return s.split(',')
 
 
-def get_diff(source, target):  # type: (List[str], List[str]) -> str
-    source_lines = ''.join(source).split('\n')
-    target_lines = ''.join(target).split('\n')
-    d = difflib.Differ()
-    diff = d.compare(source_lines, target_lines)
-    return '\n'.join(diff)
+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))
+    print(diff)
+    return diff
 
 
 def main(argv=None):  # type: (Optional[Sequence[str]]) -> int
@@ -105,14 +105,6 @@ def main(argv=None):  # type: (Optional[Sequence[str]]) -> int
         default=[],
         help='Ordered list of keys to keep at the top of JSON hashes',
     )
-    parser.add_argument(
-        '--show-expected',
-        action='store_true',
-        dest='show_expected',
-        default=False,
-        help='Show a diff between the input file and expected (pretty) output',
-    )
-
     parser.add_argument('filenames', nargs='*', help='Filenames to fix')
     args = parser.parse_args(argv)
 
@@ -131,11 +123,10 @@ def main(argv=None):  # type: (Optional[Sequence[str]]) -> int
             if contents != pretty_contents:
                 print('File {} is not pretty-formatted'.format(json_file))
 
-                if args.show_expected:
-                    print(get_diff(contents, list(pretty_contents)))
-
                 if args.autofix:
                     _autofix(json_file, pretty_contents)
+                else:
+                    print(get_diff(''.join(contents), pretty_contents))
 
                 status = 1
         except ValueError:

tests/pretty_format_json_test.py

@@ -3,7 +3,6 @@ import shutil
 import pytest
 from six import PY2
 
-from pre_commit_hooks.pretty_format_json import get_diff
 from pre_commit_hooks.pretty_format_json import main
 from pre_commit_hooks.pretty_format_json import parse_num_to_int
 from testing.util import get_resource_path
@@ -108,76 +107,51 @@ def test_badfile_main():
     assert ret == 1
 
 
-def test_diffing_output():
-    table_tests = [
-        {
-            'name': 'diff_test_1',
-            'source': """
-{
-    "key1": "val1",
-    "key2":   2,
-"array_key": [1, 2, 3],
-        "object":{
-        "bool_key": true
-      }
-}
-""",
-            'target': """
-{
-  "array_key": [
-    1,
-    2,
-    3
-  ],
-  "key1": "val1",
-  "key2": 2,
-  "object": {
-    "bool_key": true
-  }
-}
-""",
-            'expected': """
-{
-+   "array_key": [
-+     1,
+def test_diffing_output(capsys):
+    resource_path = get_resource_path('not_pretty_formatted_json.json')
+    expected_retval = 1
+    expected_diff = '''
+  {
+-     "foo":
+-     "bar",
+-         "alist": [2, 34, 234],
++   "alist": [
 +     2,
-+     3
++     34,
++     234
 +   ],
--     "key1": "val1",
-? --
-
-+   "key1": "val1",
--     "key2":   2,
-? --          --
-
-+   "key2": 2,
-- "array_key": [1, 2, 3],
--         "object":{
-? ------
-
-+   "object": {
-?            +
-
--         "bool_key": true
-? ----
-
-+     "bool_key": true
--       }
-+   }
+-   "blah": null
++   "blah": null,
+?               +
++   "foo": "bar"
   }
-""",
-        },
-        {
-            'name': 'diff_test_2',
-            'source': '',
-            'target': '',
-            'expected': '',
-        },
 
-    ]
-    for test in table_tests:
-        s = list(test['source'])
-        t = list(test['target'])
-        expected = test['expected'].strip()
-        actual = get_diff(s, t).strip()
-        assert actual == expected
+  {
+-     "foo":
+-     "bar",
+-         "alist": [2, 34, 234],
++   "alist": [
++     2,
++     34,
++     234
++   ],
+-   "blah": null
++   "blah": null,
+?               +
++   "foo": "bar"
+  }
+
+
+'''
+    # output should include a line with the filepath, build it here
+    file_output_line = 'File {} is not pretty-formatted'.format(resource_path)
+    # prepend the above line to the diff
+    expected_output = file_output_line + expected_diff
+
+    actual_retval = main([resource_path])
+    actual_output = capsys.readouterr()
+
+    assert actual_retval == expected_retval
+
+    actual_output = '\n'.join(actual_output)
+    assert actual_output == expected_output