Return True from validate_national_checksum on success (#290)

BBAN.validate_national_checksum() returned False when the national checksum
was valid, while the no-checksum-algorithm branch returned True for the same
'valid' meaning. As documented, the method raises on an invalid checksum, so
the boolean return should be True when the checksum is valid. A valid IBAN
such as BE68539007547034 therefore wrongly reported False.

Author: gaoflow

schwifty/bban.py

@@ -251,7 +251,7 @@ def validate_national_checksum(self) -> bool:
         components = [self._get_component(component) for component in algo.accepts]
         if not algo.validate(components, self.national_checksum_digits):
             raise exceptions.InvalidBBANChecksum("Invalid national checksum")
-        return False
+        return True
 
     def _get_component(self, component_type: Component) -> str:
         position = _get_position_range(self.spec, component_type)

tests/test_bban.py

@@ -1,6 +1,16 @@
 import pytest
 
 from schwifty.bban import BBAN
+from schwifty.exceptions import InvalidBBANChecksum
+
+
+def test_validate_national_checksum() -> None:
+    # A valid national checksum returns True (consistent with the "no checksum
+    # algorithm" case), while an invalid one raises InvalidBBANChecksum.
+    assert BBAN("BE", "539007547034").validate_national_checksum() is True
+    assert BBAN("GB", "WEST12345698765432").validate_national_checksum() is True
+    with pytest.raises(InvalidBBANChecksum):
+        BBAN("BE", "539007547035").validate_national_checksum()
 
 
 @pytest.mark.parametrize("country_code", ["DE", "ES", "GB", "FR", "PL"])