fix: Setting.set was incorrectly instanciating ValidationError.

bonobo/settings.py

@@ -31,7 +31,7 @@ class Setting:
     def __init__(self, name, default=None, validator=None, formatter=None):
         self.name = name
 
-        if default:
+        if default is not None:
             self.default = default if callable(default) else lambda: default
         else:
             self.default = lambda: None
@@ -51,7 +51,7 @@ class Setting:
     def set(self, value):
         value = self.formatter(value) if self.formatter else value
         if self.validator and not self.validator(value):
-            raise ValidationError('Invalid value {!r} for setting {}.'.format(value, self.name))
+            raise ValidationError(self, 'Invalid value {!r} for setting {}.'.format(value, self.name))
         self.value = value
 
     def set_if_true(self, value):

tests/test_settings.py

@@ -5,6 +5,7 @@ from unittest.mock import patch
 import pytest
 
 from bonobo import settings
+from bonobo.errors import ValidationError
 
 TEST_SETTING = 'TEST_SETTING'
 
@@ -38,6 +39,15 @@ def test_setting():
         s.clear()
         assert s.get() == 'hello'
 
+    s = settings.Setting(TEST_SETTING, default=0, validator=lambda x: x == 42)
+    with pytest.raises(ValidationError):
+        assert s.get() is 0
+
+    s.set(42)
+
+    with pytest.raises(ValidationError):
+        s.set(21)
+
 
 def test_default_settings():
     settings.clear_all()