fix: Validate domain is present when calling set_provider on registry

It is incorrect to call `ProviderRegister.set_provider` without a
provider AND a domain. A validation check exists for the provider, but
none for the domain.

In this commit, we introduce that domain validation and introduce tests
to capture this expected behavior.

Signed-off-by: Matthew Keeler <mkeeler@launchdarkly.com>

Author: keelerm84

openfeature/provider/_registry.py

@@ -24,6 +24,8 @@ def __init__(self) -> None:
     def set_provider(self, domain: str, provider: FeatureProvider) -> None:
         if provider is None:
             raise GeneralError(error_message="No provider")
+        if domain is None:
+            raise GeneralError(error_message="No domain")
         providers = self._providers
         if domain in providers:
             old_provider = providers[domain]

tests/provider/test_registry.py

@@ -0,0 +1,118 @@
+from unittest.mock import Mock
+
+from openfeature.exception import GeneralError
+from openfeature.provider._registry import ProviderRegistry
+from openfeature.provider.no_op_provider import NoOpProvider
+
+
+def test_registry_serves_noop_as_default():
+    registry = ProviderRegistry()
+
+    assert isinstance(registry.get_default_provider(), NoOpProvider)
+    assert isinstance(registry.get_provider("unknown domain"), NoOpProvider)
+
+
+def test_setting_provider_requires_domain():
+    registry = ProviderRegistry()
+
+    try:
+        registry.set_provider(None, NoOpProvider())  # type: ignore[reportArgumentType]
+        raise AssertionError(
+            "Expected an exception when setting provider with None domain"
+        )
+    except GeneralError as e:
+        assert e.error_message == "No domain"
+    except Exception as e:
+        raise AssertionError("Expected GeneralError, got {type(e)}") from e
+
+
+def test_setting_provider_requires_provider():
+    registry = ProviderRegistry()
+
+    try:
+        registry.set_provider("domain", None)  # type: ignore[reportArgumentType]
+        raise AssertionError("Expected an exception when setting provider to None")
+    except GeneralError as e:
+        assert e.error_message == "No provider"
+    except Exception as e:
+        raise AssertionError("Expected GeneralError, got {type(e)}") from e
+
+
+def test_can_register_provider_to_multiple_domains():
+    registry = ProviderRegistry()
+    provider = NoOpProvider()
+
+    registry.set_provider("domain1", provider)
+    registry.set_provider("domain2", provider)
+
+    assert registry.get_provider("domain1") is provider
+    assert registry.get_provider("domain2") is provider
+
+
+def test_registering_provider_replaces_previous_provider():
+    """Test that registering a provider replaces the previous provider and calls shutdown on the old one."""
+
+    registry = ProviderRegistry()
+    provider1 = Mock()
+    provider2 = Mock()
+
+    registry.set_provider("domain", provider1)
+    assert registry.get_provider("domain") is provider1
+
+    registry.set_provider("domain", provider2)
+    assert registry.get_provider("domain") is provider2
+
+    provider1.shutdown.assert_called_once()
+    provider2.shutdown.assert_not_called()
+
+
+def test_registering_provider_for_first_time_initializes_it():
+    """Test that registering a provider for the first time calls its initialize method."""
+
+    registry = ProviderRegistry()
+    provider = Mock()
+
+    registry.set_provider("domain1", provider)
+    registry.set_provider("domain2", provider)
+
+    provider.initialize.assert_called_once()
+
+
+def test_setting_default_provider_requires_provider():
+    registry = ProviderRegistry()
+
+    try:
+        registry.set_default_provider(None)  # type: ignore[reportArgumentType]
+        raise AssertionError(
+            "Expected an exception when setting default provider to None"
+        )
+    except GeneralError as e:
+        assert e.error_message == "No provider"
+    except Exception as e:
+        raise AssertionError("Expected GeneralError, got {type(e)}") from e
+
+
+def test_replacing_default_provider_shuts_down_old_one():
+    """Test that replacing the default provider shuts down the old default provider."""
+
+    registry = ProviderRegistry()
+    default_provider1 = Mock()
+    default_provider2 = Mock()
+
+    registry.set_default_provider(default_provider1)
+    assert registry.get_default_provider() is default_provider1
+
+    registry.set_default_provider(default_provider2)
+    assert registry.get_default_provider() is default_provider2
+
+    default_provider1.shutdown.assert_called_once()
+    default_provider2.shutdown.assert_not_called()
+
+
+def test_setting_default_provider_initializes_it():
+    registry = ProviderRegistry()
+    provider = Mock()
+
+    registry.set_default_provider(provider)
+
+    provider.initialize.assert_called_once()