Raise ValidationError from the config test validators

`frequenz-quantities` 1.0.2 changed its `marshmallow` optional dependency
floor from `< 4` to `>= 4` (frequenz-floss/frequenz-quantities-python#107),
correcting metadata that had been wrong since that library was ported to
`marshmallow` 4.  That cap was the only thing holding us on `marshmallow`
3, as our own requirement has allowed `< 5` since 870e880, so CI now
resolves `marshmallow` 4.

`marshmallow` 4 removed support for validators that signal failure by
returning `False`, deprecated in 3.24.0:

    Custom validators must raise a `ValidationError` for invalid values
    (deprecated in 3.24.0).  Returning `False` is no longer supported.

The configuration test dataclasses used exactly that pattern, a
`lambda s: s.startswith("test")` in the field metadata.  The validator is
still registered and still called, only its return value is ignored, so
the invalid value is accepted and `test_load_config_dataclass` and
`test_new_receiver_configurations[Validation Error]` fail.

Replacing the lambdas with a function that raises restores the checks.
The message stays `Invalid value.`, which is what `marshmallow` 3 emitted
through its `validator_failed` error key, so the expected output in
`test_manager.py` is unchanged and the surrounding test cases remain
consistent in asserting on `marshmallow`'s stock messages.

Nothing under `src/` needed changing: the validators there are
`marshmallow.validate.Range` and `OneOf`, which already raise.  A raising
validator also works on `marshmallow` 3, so the supported range is not
narrowed, but the same silent acceptance can hit users who wrote their
own boolean validators, hence the release notes entry.

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

Author: llucax

RELEASE_NOTES.md

@@ -6,6 +6,8 @@
 
 ## Upgrading
 
+- Custom validators passed through a configuration dataclass field's `metadata` (as used by `load_config()` and `ConfigManager.new_receiver()`) must now raise a `marshmallow.ValidationError` to reject a value. `marshmallow` 4 removed support for validators that signal failure by returning `False`, so such validators are now ignored and the invalid value is accepted silently. This affects you as soon as `marshmallow` 4 is installed, which `frequenz-quantities` 1.0.2 and later require.
+
 <!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
 
 ## New Features

tests/config/test_manager.py

@@ -20,11 +20,24 @@
 from frequenz.sdk.config._manager import _get_key
 
 
+def _validate_name(value: str) -> None:
+    """Validate that a name starts with `test`.
+
+    Args:
+        value: The name to validate.
+
+    Raises:
+        marshmallow.ValidationError: If the name doesn't start with `test`.
+    """
+    if not value.startswith("test"):
+        raise marshmallow.ValidationError("Invalid value.")
+
+
 @dataclass
 class SimpleConfig:
     """A simple configuration class for testing."""
 
-    name: str = dataclasses.field(metadata={"validate": lambda s: s.startswith("test")})
+    name: str = dataclasses.field(metadata={"validate": _validate_name})
     value: int
 
 

tests/config/test_util.py

@@ -14,19 +14,32 @@
 from frequenz.sdk.config._util import load_config
 
 
+def _validate_name(value: str) -> None:
+    """Validate that a name starts with `test`.
+
+    Args:
+        value: The name to validate.
+
+    Raises:
+        marshmallow.ValidationError: If the name doesn't start with `test`.
+    """
+    if not value.startswith("test"):
+        raise marshmallow.ValidationError("Invalid value.")
+
+
 @dataclasses.dataclass
 class SimpleConfig:
     """A simple configuration class for testing."""
 
-    name: str = dataclasses.field(metadata={"validate": lambda s: s.startswith("test")})
+    name: str = dataclasses.field(metadata={"validate": _validate_name})
     value: int
 
 
 @marshmallow_dataclass.dataclass
 class MmSimpleConfig:
     """A simple marshmallow_dataclass configuration class for testing."""
 
-    name: str = dataclasses.field(metadata={"validate": lambda s: s.startswith("test")})
+    name: str = dataclasses.field(metadata={"validate": _validate_name})
     value: int