file-contents-sorter should add newline at end of files missing newlines

Make an explicit 'else' path for readability

pre_commit_hooks/file_contents_sorter.py

@@ -18,18 +18,19 @@ FAIL = 1
 
 
 def sort_file_contents(f):
-    before = [line.strip(b'\n\r') for line in f if line.strip()]
-    after = sorted(before)
-
-    if before == after:
-        return PASS
+    before = list(f)
+    after = sorted([line.strip(b'\n\r') for line in before if line.strip()])
 
+    before_string = b''.join(before)
     after_string = b'\n'.join(after) + b'\n'
 
-    f.seek(0)
-    f.write(after_string)
-    f.truncate()
-    return FAIL
+    if before_string == after_string:
+        return PASS
+    else:
+        f.seek(0)
+        f.write(after_string)
+        f.truncate()
+        return FAIL
 
 
 def main(argv=None):

tests/file_contents_sorter_test.py

@@ -8,18 +8,18 @@ from pre_commit_hooks.file_contents_sorter import PASS
 @pytest.mark.parametrize(
     ('input_s', 'expected_retval', 'output'),
     (
-        (b'', PASS, b''),
+        (b'', FAIL, b'\n'),
         (b'lonesome\n', PASS, b'lonesome\n'),
-        (b'missing_newline', PASS, b'missing_newline'),
+        (b'missing_newline', FAIL, b'missing_newline\n'),
         (b'newline\nmissing', FAIL, b'missing\nnewline\n'),
-        (b'missing\nnewline', PASS, b'missing\nnewline'),
+        (b'missing\nnewline', FAIL, b'missing\nnewline\n'),
         (b'alpha\nbeta\n', PASS, b'alpha\nbeta\n'),
         (b'beta\nalpha\n', FAIL, b'alpha\nbeta\n'),
         (b'C\nc\n', PASS, b'C\nc\n'),
         (b'c\nC\n', FAIL, b'C\nc\n'),
         (b'mag ical \n tre vor\n', FAIL, b' tre vor\nmag ical \n'),
         (b'@\n-\n_\n#\n', FAIL, b'#\n-\n@\n_\n'),
-        (b'extra\n\n\nwhitespace\n', PASS, b'extra\n\n\nwhitespace\n'),
+        (b'extra\n\n\nwhitespace\n', FAIL, b'extra\nwhitespace\n'),
         (b'whitespace\n\n\nextra\n', FAIL, b'extra\nwhitespace\n'),
     )
 )