diff --git a/tests/test_core/__init__.py b/tests/test_core/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_core/test_registry.py b/tests/test_core/test_registry.py
new file mode 100644
index 0000000..505dbcb
--- /dev/null
+++ b/tests/test_core/test_registry.py
@@ -0,0 +1,294 @@
+"""Tests for the Registry and SimpleRegistry classes.
+
+Covers:
+- SimpleRegistry: registration, retrieval, and membership checks.
+- Registry: decorator-based registration, config type tracking,
+  discriminator-based dispatch, and error handling.
+"""
+
+from typing import Literal
+
+import pytest
+from pydantic import BaseModel
+
+from batdetect2.core.registries import Registry, SimpleRegistry
+
+
+class TestSimpleRegistry:
+    def test_register_and_get(self):
+        """Registered objects can be retrieved by name."""
+        registry = SimpleRegistry("test")
+
+        @registry.register("my_item")
+        def item():
+            return 42
+
+        assert registry.get("my_item")() == 42
+
+    def test_register_returns_original_object(self):
+        """The register decorator returns the decorated object unchanged."""
+        registry = SimpleRegistry[int]("test")
+
+        @registry.register("x")
+        def fn() -> int:
+            return 7
+
+        assert fn() == 7
+
+    def test_has_returns_true_for_registered_name(self):
+        """has() returns True for a name that was registered."""
+        registry = SimpleRegistry("test")
+        registry.register("present")(lambda: None)
+        assert registry.has("present") is True
+
+    def test_has_returns_false_for_unknown_name(self):
+        """has() returns False for a name that was never registered."""
+        registry = SimpleRegistry("test")
+        assert registry.has("absent") is False
+
+    def test_get_raises_for_unknown_name(self):
+        """get() raises KeyError for an unregistered name."""
+        registry = SimpleRegistry("test")
+        with pytest.raises(KeyError):
+            registry.get("nonexistent")
+
+    def test_register_overwrites_existing_entry(self):
+        """Re-registering the same name replaces the previous entry."""
+        registry = SimpleRegistry("test")
+        registry.register("key")(lambda: 1)
+        registry.register("key")(lambda: 2)
+        assert registry.get("key")() == 2
+
+    def test_multiple_items_registered_independently(self):
+        """Multiple items can be registered without interfering."""
+        registry = SimpleRegistry("test")
+        registry.register("a")(lambda: "a")
+        registry.register("b")(lambda: "b")
+        assert registry.get("a")() == "a"
+        assert registry.get("b")() == "b"
+
+
+class TestRegistryRegister:
+    def test_register_makes_factory_callable_via_build(self):
+        """A registered factory is reachable through build()."""
+
+        class DummyConfig(BaseModel):
+            name: Literal["dummy"] = "dummy"
+            value: int = 0
+
+        class DummyOutput:
+            def __init__(self, config: DummyConfig):
+                self.config = config
+
+        registry: Registry[DummyOutput, []] = Registry("test")
+        registry.register(DummyConfig)(lambda c: DummyOutput(c))
+        result = registry.build(DummyConfig(value=3))
+        assert isinstance(result, DummyOutput)
+        assert result.config.value == 3
+
+    def test_register_makes_config_type_retrievable(self):
+        """A registered config type is reachable through get_config_type()."""
+
+        class DummyConfig(BaseModel):
+            name: Literal["dummy"] = "dummy"
+            value: int = 0
+
+        registry: Registry[object, []] = Registry("test")
+        registry.register(DummyConfig)(lambda c: c)
+        assert registry.get_config_type("dummy") is DummyConfig
+
+    def test_register_raises_when_discriminator_field_missing(self):
+        """ValueError is raised if config has no discriminator field."""
+
+        class ConfigWithoutDiscriminator(BaseModel):
+            unrelated_field: str = "hello"
+
+        registry: Registry[object, []] = Registry("test")
+        with pytest.raises(ValueError, match="'name' field"):
+            registry.register(ConfigWithoutDiscriminator)(lambda c: c)
+
+    def test_register_raises_when_discriminator_is_not_string(self):
+        """ValueError is raised if the discriminator default is not a str."""
+
+        class ConfigWithNonStringDiscriminator(BaseModel):
+            name: int = 42
+
+        registry: Registry[object, []] = Registry("test")
+        with pytest.raises(ValueError, match="'name' field must be a string"):
+            registry.register(ConfigWithNonStringDiscriminator)(lambda c: c)
+
+    def test_register_uses_custom_discriminator_field(self):
+        """Registry respects a non-default discriminator field name."""
+
+        class FormatConfig(BaseModel):
+            format: Literal["fmt"] = "fmt"
+
+        registry: Registry[object, []] = Registry(
+            "test", discriminator="format"
+        )
+        registry.register(FormatConfig)(lambda c: c)
+        assert registry.get_config_type("fmt") is FormatConfig
+
+    def test_register_decorator_returns_original_function(self):
+        """The register decorator returns the wrapped function unchanged."""
+
+        class DummyConfig(BaseModel):
+            name: Literal["dummy"] = "dummy"
+            value: int = 0
+
+        class DummyOutput:
+            def __init__(self, config: DummyConfig):
+                self.config = config
+
+        registry: Registry[DummyOutput, []] = Registry("test")
+
+        def factory(config: DummyConfig) -> DummyOutput:
+            return DummyOutput(config)
+
+        returned = registry.register(DummyConfig)(factory)
+        assert returned is factory
+
+
+class TestRegistryConfigTypes:
+    def test_get_config_types_returns_all_registered_types(self):
+        """get_config_types() returns every registered config class."""
+
+        class DummyConfig(BaseModel):
+            name: Literal["dummy"] = "dummy"
+
+        class AnotherConfig(BaseModel):
+            name: Literal["another"] = "another"
+
+        registry: Registry[object, []] = Registry("test")
+        registry.register(DummyConfig)(lambda c: c)
+        registry.register(AnotherConfig)(lambda c: c)
+        config_types = registry.get_config_types()
+        assert DummyConfig in config_types
+        assert AnotherConfig in config_types
+
+    def test_get_config_types_empty_when_nothing_registered(self):
+        """get_config_types() returns empty tuple for a fresh registry."""
+        registry: Registry[object, []] = Registry("test")
+        assert registry.get_config_types() == ()
+
+    def test_get_config_type_returns_correct_class(self):
+        """get_config_type() returns the class registered under a key."""
+
+        class DummyConfig(BaseModel):
+            name: Literal["dummy"] = "dummy"
+
+        registry: Registry[object, []] = Registry("test")
+        registry.register(DummyConfig)(lambda c: c)
+        assert registry.get_config_type("dummy") is DummyConfig
+
+    def test_get_config_type_raises_for_unknown_key(self):
+        """get_config_type() raises ValueError for an unregistered key."""
+        registry: Registry[object, []] = Registry("test")
+        with pytest.raises(
+            ValueError, match="No config type with name 'unknown'"
+        ):
+            registry.get_config_type("unknown")
+
+    def test_get_config_type_error_message_lists_existing_keys(self):
+        """ValueError message includes the names of registered keys."""
+
+        class DummyConfig(BaseModel):
+            name: Literal["dummy"] = "dummy"
+
+        registry: Registry[object, []] = Registry("test")
+        registry.register(DummyConfig)(lambda c: c)
+        with pytest.raises(ValueError, match="dummy"):
+            registry.get_config_type("missing")
+
+
+class TestRegistryBuild:
+    def test_build_dispatches_to_correct_factory(self):
+        """build() calls the factory registered for the config's discriminator."""
+
+        class DummyConfig(BaseModel):
+            name: Literal["dummy"] = "dummy"
+            value: int = 0
+
+        class DummyOutput:
+            def __init__(self, config: DummyConfig):
+                self.config = config
+
+        registry: Registry[DummyOutput, []] = Registry("test")
+        registry.register(DummyConfig)(lambda c: DummyOutput(c))
+
+        config = DummyConfig(value=99)
+        result = registry.build(config)
+
+        assert isinstance(result, DummyOutput)
+        assert result.config.value == 99
+
+    def test_build_dispatches_to_correct_factory_among_multiple(self):
+        """build() picks the right factory when several are registered."""
+
+        class DummyConfig(BaseModel):
+            name: Literal["dummy"] = "dummy"
+
+        class AnotherConfig(BaseModel):
+            name: Literal["another"] = "another"
+
+        class DummyOutput:
+            def __init__(self, config: DummyConfig):
+                self.config = config
+
+        class AnotherOutput:
+            def __init__(self, config: AnotherConfig):
+                self.config = config
+
+        registry: Registry[object, []] = Registry("test")
+        registry.register(DummyConfig)(lambda c: DummyOutput(c))
+        registry.register(AnotherConfig)(lambda c: AnotherOutput(c))
+
+        assert isinstance(registry.build(DummyConfig()), DummyOutput)
+        assert isinstance(registry.build(AnotherConfig()), AnotherOutput)
+
+    def test_build_raises_not_implemented_for_unregistered_format(self):
+        """build() raises NotImplementedError for an unregistered discriminator."""
+        registry: Registry[object, []] = Registry("test")
+
+        class UnknownConfig(BaseModel):
+            name: Literal["unknown"] = "unknown"
+
+        with pytest.raises(NotImplementedError, match="'unknown'"):
+            registry.build(UnknownConfig())
+
+    def test_build_passes_config_to_factory(self):
+        """build() passes the exact config object through to the factory."""
+
+        class DummyConfig(BaseModel):
+            name: Literal["dummy"] = "dummy"
+            value: int = 0
+
+        registry: Registry[DummyConfig, []] = Registry("test")
+        received: list[DummyConfig] = []
+        registry.register(DummyConfig)(lambda c: received.append(c) or c)
+
+        config = DummyConfig(value=7)
+        registry.build(config)
+
+        assert received == [config]
+
+    def test_build_uses_custom_discriminator_field(self):
+        """build() resolves the factory using the configured discriminator."""
+
+        class FormatConfig(BaseModel):
+            format: Literal["fmt"] = "fmt"
+
+        registry: Registry[str, []] = Registry("test", discriminator="format")
+        registry.register(FormatConfig)(lambda c: "fmt_result")
+
+        assert registry.build(FormatConfig()) == "fmt_result"
+
+    def test_build_error_message_includes_registry_name(self):
+        """NotImplementedError message names the registry for easier debugging."""
+        registry: Registry[object, []] = Registry("my_registry")
+
+        class UnknownConfig(BaseModel):
+            name: Literal["ghost"] = "ghost"
+
+        with pytest.raises(NotImplementedError, match="my_registry"):
+            registry.build(UnknownConfig())