Implement --check option

cli.py

@@ -35,6 +35,11 @@ if __name__ == '__main__':
         '--funky', '-f', action='store_true',
         help='List filenames with special characters'
     )
+    mgroup.add_argument(
+        '--check', '-c', action='store_true',
+        help='Check whether a name is normalised or not'
+    )
+
     parser.add_argument(
         'files', type=str, nargs='+',
         help='File(s) to normalise the name of (relative or absolute path).'
@@ -59,14 +64,24 @@ if __name__ == '__main__':
         whitelist = whitelist.difference(set(args.disallow))
 
     # define operations
-    listchanges = lambda a, b: print('{}{} -->    {}'.format(a, ' '*(60-len(a)), b))
-    listfunky = lambda a, b: print(a)
+    def listchanges(before, after):
+        print(f'{after}{" "*(60-len(after))} -->    {before}')
+
+    def listfunky(before, _):
+        print(before)
+
+    def checkname(before, after):
+        if before != after:
+            sys.exit(1)
+        sys.exit(0)
 
     operation = rename
     if args.dryrun:
         operation = listchanges
     elif args.funky:
         operation = listfunky
+    elif args.check:
+        operation = checkname
 
     # do what needs to be done
     Normalisename(operation, args.separator, whitelist)(args.files)