✨ feat: implement value object simple class and its unit tests

tests/models/test_value_object_get_attribute.py

@@ -0,0 +1,48 @@
+"""
+Test value object module.
+"""
+
+from object_mother_pattern.mothers import IntegerMother
+from pytest import mark, raises as assert_raises
+
+from value_object_pattern import ValueObject
+
+
+class IntegerValueObject(ValueObject[int]):
+    """
+    IntegerValueObject value object class.
+    """
+
+
+@mark.unit_testing
+def test_value_object_get_attribute() -> None:
+    """
+    Test that a value object value can be accessed.
+    """
+    value_object = IntegerValueObject(value=IntegerMother.create())
+
+    value_object.value  # noqa: B018
+
+
+@mark.unit_testing
+def test_value_object_get_protected_attribute() -> None:
+    """
+    Test that a value object protected value can be accessed.
+    """
+    value_object = IntegerValueObject(value=IntegerMother.create())
+
+    value_object._value  # noqa: B018
+
+
+@mark.unit_testing
+def test_value_object_cannot_get_unexistent_attribute() -> None:
+    """
+    Test that a value object value cannot be modified after initialization.
+    """
+    value_object = IntegerValueObject(value=IntegerMother.create())
+
+    with assert_raises(
+        expected_exception=AttributeError,
+        match=f"'{value_object.__class__.__name__}' object has no attribute 'not_existent_attribute'",
+    ):
+        value_object.not_existent_attribute  # type: ignore[attr-defined]  # noqa: B018

tests/models/test_value_object_set_attribute.py

@@ -0,0 +1,56 @@
+"""
+Test value object module.
+"""
+
+from object_mother_pattern.mothers import IntegerMother
+from pytest import mark, raises as assert_raises
+
+from value_object_pattern import ValueObject
+
+
+class IntegerValueObject(ValueObject[int]):
+    """
+    IntegerValueObject value object class.
+    """
+
+
+@mark.unit_testing
+def test_value_object_cannot_modify_value() -> None:
+    """
+    Test that a value object value cannot be modified after initialization.
+    """
+    value_object = IntegerValueObject(value=IntegerMother.create())
+
+    with assert_raises(
+        expected_exception=AttributeError,
+        match='Cannot modify attribute "value" of immutable instance',
+    ):
+        value_object.value = IntegerMother.create()  # type: ignore[misc]
+
+
+@mark.unit_testing
+def test_value_object_cannot_modify_protected_value() -> None:
+    """
+    Test that a value object protected value cannot be modified after initialization.
+    """
+    value_object = IntegerValueObject(value=IntegerMother.create())
+
+    with assert_raises(
+        expected_exception=AttributeError,
+        match='Cannot modify attribute "_value" of immutable instance',
+    ):
+        value_object._value = IntegerMother.create()
+
+
+@mark.unit_testing
+def test_value_object_cannot_add_new_attribute() -> None:
+    """
+    Test that cannot add a new attribute to a value object after initialization.
+    """
+    value_object = IntegerValueObject(value=IntegerMother.create())
+
+    with assert_raises(
+        expected_exception=AttributeError,
+        match=f'{value_object.__class__.__name__} object has no attribute "new_attribute"',
+    ):
+        value_object.new_attribute = IntegerMother.create()

value_object_pattern/__init__.py

@@ -1 +1,5 @@
 __version__ = '2025.01.02'
+
+from .models import ValueObject
+
+__all__ = ('ValueObject',)

value_object_pattern/models/__init__.py

@@ -0,0 +1,3 @@
+from .value_object import ValueObject
+
+__all__ = ('ValueObject',)

value_object_pattern/models/value_object.py

@@ -0,0 +1,108 @@
+"""
+Value object generic type.
+"""
+
+from abc import ABC
+from typing import Generic, NoReturn, TypeVar, override
+
+T = TypeVar('T')
+
+
+class ValueObject(ABC, Generic[T]):
+    """
+    ValueObject generic type.
+    """
+
+    __slots__ = ('_value',)
+    __match_args__ = ('_value',)
+
+    _value: T
+
+    def __init__(self, *, value: T) -> None:
+        """
+        ValueObject value object constructor.
+
+        Args:
+            value (T): Value.
+        """
+        object.__setattr__(self, '_value', value)
+
+    @override
+    def __repr__(self) -> str:
+        """
+        Returns a detailed string representation of the value object.
+
+        Returns:
+            str: A string representation of the value object in the format 'ClassName(value=value)'.
+        """
+        return f'{self.__class__.__name__}(value={self._value!s})'
+
+    @override
+    def __str__(self) -> str:
+        """
+        Returns a simple string representation of the value object.
+
+        Returns:
+            str: The string representation of the value object value.
+        """
+        return str(object=self._value)
+
+    @override
+    def __hash__(self) -> int:
+        """
+        Returns the hash of the value object.
+
+        Returns:
+            int: Hash of the value object.
+        """
+        return hash(self._value)
+
+    @override
+    def __eq__(self, other: object) -> bool:
+        """
+        Check if the value object is equal to another value object.
+
+        Args:
+            other (object): Object to compare.
+
+        Returns:
+            bool: True if both objects are equal, otherwise False.
+        """
+        if not isinstance(other, self.__class__):
+            return NotImplemented
+
+        return self._value == other.value
+
+    @override
+    def __setattr__(self, key: str, value: T) -> NoReturn:
+        """
+        Prevents modification or addition of attributes in the value object.
+
+        Args:
+            key (str): The name of the attribute.
+            value (T): The value to be assigned to the attribute.
+
+        Raises:
+            AttributeError: If there is an attempt to modify an existing attribute.
+            AttributeError: If there is an attempt to add a new attribute.
+        """
+        public_key = key.replace('_', '')
+        public_slots1 = [slot.replace('_', '') for slot in self.__slots__]
+
+        if key in self.__slots__:
+            raise AttributeError(f'Cannot modify attribute "{key}" of immutable instance.')
+
+        if public_key in public_slots1:
+            raise AttributeError(f'Cannot modify attribute "{public_key}" of immutable instance.')
+
+        raise AttributeError(f'{self.__class__.__name__} object has no attribute "{key}".')
+
+    @property
+    def value(self) -> T:
+        """
+        Returns the value object value.
+
+        Returns:
+            T: The value object value.
+        """
+        return self._value