model.base: fix id_short validation

This commit backports 445b1d8f from fix/id_short_validation (!78 (merged)).

In RegEx, the $ asserts the end of a string or line. When used in re.match() it asserts the end of the string by default, unless the last character is a newline symbol (\n). Then it asserts the end of the string before the newline. Thus the first regex check doesn't filter valid id_shorts ending in a newline, which it should. See https://docs.python.org/3.9/library/re.html#index-2

Using re.fullmatch() instead fixes this issue, making the ^ and $ unnecessary as well.

Next to adding a test for this behaviour this commit also simplifies the check for an alphabetical character at the start of the id_short. And although both checks could also be merged into one, they are left separate to be able to report more accurate errors.

aas/model/base.py

@@ -461,9 +461,9 @@ class Referable(metaclass=abc.ABCMeta):
         if id_short is None and not hasattr(self, 'identification'):
             raise ValueError("The id_short for not identifiable elements is mandatory")
         test_id_short: str = str(id_short)
-        if not re.match("^[a-zA-Z0-9_]*$", test_id_short):
+        if not re.fullmatch("[a-zA-Z0-9_]*", test_id_short):
             raise ValueError("The id_short must contain only letters, digits and underscore")
-        if not re.match("^([a-zA-Z].*|)$", test_id_short):
+        if len(test_id_short) > 0 and not test_id_short[0].isalpha():
             raise ValueError("The id_short must start with a letter")
 
         if self.parent is not None and id_short != self.id_short: