Fix broken uppercase capture group test

Important: Python regex flags such as multiline need to be specified
in the compiled regex and not afterwards.

Author: mjbear

tests/test_capture_group_case.py

@@ -9,7 +9,7 @@
 
 # https://github.com/google/textfsm/wiki/TextFSM#value-definitions
 OPTION_KEYWORDS = ["Filldown", "Key", "Required", "List", "Fillup"]
-RE_CAPGRP = re.compile(rf"^Value\s+(?:(?:(?:{'|'.join(OPTION_KEYWORDS)}),?)+\s+)?(\S+)")  # noqa: E231
+RE_CAPGRP = re.compile(rf"^Value\s+(?:(?:(?:{'|'.join(OPTION_KEYWORDS)}),?)+\s+)?(\S+)", re.MULTILINE)  # noqa: E231
 
 
 def return_template_files():
@@ -27,12 +27,15 @@ def return_template_capture_groups(template_file):
     """Return a list of capture groups in a template."""
     with open(template_file, encoding="utf-8") as fh:
         file = fh.read()
-        return RE_CAPGRP.findall(file, re.MULTILINE)
+        return RE_CAPGRP.findall(file)
 
 
 def test_uppercase_capture_group(load_template_files):
     """Test that the capture groups are uppercase."""
     capture_groups = return_template_capture_groups(load_template_files)
 
+    # catch non-functional regexes and re function syntax which match nothing
+    assert capture_groups != [], 'No capture groups were matched, check regex function syntax/usage'
+
     for group in capture_groups:
         assert group.isupper()