unicode_rules: Use back-ticks for printing literal chars/strings

cylc/flow/unicode_rules.py

@@ -23,9 +23,9 @@
 ENGLISH_REGEX_MAP = {
     r'\w': 'alphanumeric',
     r'a-zA-Z0-9': 'latin letters and numbers',
-    r'\-': '-',
-    r'\.': '.',
-    r'\/': '/'
+    r'\-': '``-``',
+    r'\.': '``.``',
+    r'\/': '``/``'
 }
 
 
@@ -39,10 +39,12 @@ def regex_chars_to_text(chars):
         ['-', '.', '/']
         >>> regex_chars_to_text([r'\w'])
         ['alphanumeric']
+        >>> regex_chars_to_text(['not_in_map'])
+        ['not_in_map']
 
     """
     return [
-        ENGLISH_REGEX_MAP.get(char, char)
+        ENGLISH_REGEX_MAP.get(char, f'``{char}``')
         for char in chars
     ]
 
@@ -72,7 +74,7 @@ def allowed_characters(*chars):
     Example:
         >>> regex, message = allowed_characters('a', 'b', 'c')
         >>> message
-        'can only contain: a, b, c'
+        'can only contain: ``a``, ``b``, ``c``'
         >>> bool(regex.match('abc'))
         True
         >>> bool(regex.match('def'))
@@ -91,7 +93,7 @@ def not_starts_with(*chars):
     Example:
         >>> regex, message = not_starts_with('a', 'b', 'c')
         >>> message
-        'can not start with: a, b, c'
+        'can not start with: ``a``, ``b``, ``c``'
         >>> bool(regex.match('def'))
         True
         >>> bool(regex.match('adef'))
@@ -111,7 +113,7 @@ def not_contains_colon_unless_starts_with(*chars):
         >>> regex, message = not_contain_colon_unless_starts_with(
                 'INFO', 'WARNING')
         >>> message
-        'cannot contain a colon unless starts with: INFO, WARNING'
+        'cannot contain a colon unless starts with: ``INFO``, ``WARNING``'
         >>> bool(regex.match('Foo: bar'))
         False
         >>> bool(regex.match('INFO: Foo: bar'))

tests/unit/test_suite_files.py

@@ -175,7 +175,7 @@ def get_register_test_cases():
          None,  # expected symlink
          None,  # expected return value
          SuiteServiceFileError,  # expected exception
-         "can not start with: ., -"  # expected part of exception message
+         "can not start with: ``.``, ``-``"  # expected part of exception message
          )
     ]