Add support for registering instances.

Author: runemalm

src/dependency_injection/container.py

@@ -50,6 +50,12 @@ def register_singleton(self, dependency: Type, implementation: Optional[Type] =
             raise ValueError(f"Dependency {dependency} is already registered.")
         self._registrations[dependency] = Registration(dependency, implementation, Scope.SINGLETON, tags, constructor_args)
 
+    def register_instance(self, dependency: Type, instance: Any, tags: Optional[set] = None) -> None:
+        if dependency in self._registrations:
+            raise ValueError(f"Dependency {dependency} is already registered.")
+        self._registrations[dependency] = Registration(dependency, type(instance), Scope.SINGLETON, constructor_args={}, tags=tags)
+        self._singleton_instances[dependency] = instance
+
     def resolve(self, dependency: Type, scope_name: str = DEFAULT_SCOPE_NAME) -> Type:
         if scope_name not in self._scoped_instances:
             self._scoped_instances[scope_name] = {}

tests/unit_test/container/register/test_register_instance.py

@@ -0,0 +1,44 @@
+import pytest
+
+from dependency_injection.container import DependencyContainer
+from unit_test.unit_test_case import UnitTestCase
+
+
+class TestRegisterInstance(UnitTestCase):
+
+    def test_register_instance_succeeds_when_not_previously_registered(
+        self,
+    ):
+        # arrange
+        class Vehicle:
+            pass
+
+        class Car(Vehicle):
+            pass
+
+        dependency_container = DependencyContainer.get_instance()
+        instance = Car()
+
+        # act
+        dependency_container.register_instance(Vehicle, instance)
+
+        # assert
+        # (no exception thrown)
+
+    def test_register_instance_fails_when_already_registered(
+        self,
+    ):
+        # arrange
+        class Vehicle:
+            pass
+
+        class Car(Vehicle):
+            pass
+
+        dependency_container = DependencyContainer.get_instance()
+        instance = Car()
+        dependency_container.register_instance(Vehicle, instance)
+
+        # act + assert
+        with pytest.raises(ValueError, match="is already registered"):
+            dependency_container.register_instance(Vehicle, instance)

tests/unit_test/container/resolve/test_resolve_instance.py

@@ -0,0 +1,46 @@
+from dependency_injection.container import DependencyContainer
+from unit_test.unit_test_case import UnitTestCase
+
+
+class TestResolveInstance(UnitTestCase):
+
+    def test_resolve_instance_returns_instance(
+        self,
+    ):
+        # arrange
+        class Vehicle:
+            pass
+
+        class Car(Vehicle):
+            pass
+
+        dependency_container = DependencyContainer.get_instance()
+        instance = Car()
+        dependency_container.register_instance(Vehicle, instance)
+
+        # act
+        resolved_dependency = dependency_container.resolve(Vehicle)
+
+        # assert
+        self.assertEqual(resolved_dependency, instance)
+
+    def test_resolve_instance_twice_returns_same_instance(
+        self,
+    ):
+        # arrange
+        class Vehicle:
+            pass
+
+        class Car(Vehicle):
+            pass
+
+        dependency_container = DependencyContainer()
+        instance = Car()
+        dependency_container.register_instance(Vehicle, instance)
+
+        # act
+        resolved_dependency_1 = dependency_container.resolve(Vehicle)
+        resolved_dependency_2 = dependency_container.resolve(Vehicle)
+
+        # assert
+        self.assertEqual(resolved_dependency_1, resolved_dependency_2)