diff --git a/tests/test_execution_registry.py b/tests/test_execution_registry.py
new file mode 100644
index 0000000..7d95d85
--- /dev/null
+++ b/tests/test_execution_registry.py
@@ -0,0 +1,179 @@
+from __future__ import annotations
+
+import unittest
+
+from src.execution_registry import (
+    ExecutionRegistry,
+    MirroredCommand,
+    MirroredTool,
+    build_execution_registry,
+)
+from src.commands import PORTED_COMMANDS
+from src.tools import PORTED_TOOLS
+
+
+class TestBuildExecutionRegistry(unittest.TestCase):
+    """Tests for build_execution_registry and basic registry properties."""
+
+    def test_returns_execution_registry(self) -> None:
+        registry = build_execution_registry()
+        self.assertIsInstance(registry, ExecutionRegistry)
+
+    def test_has_non_empty_commands(self) -> None:
+        registry = build_execution_registry()
+        self.assertGreater(len(registry.commands), 0)
+
+    def test_has_non_empty_tools(self) -> None:
+        registry = build_execution_registry()
+        self.assertGreater(len(registry.tools), 0)
+
+    def test_command_count_matches_ported_commands(self) -> None:
+        registry = build_execution_registry()
+        self.assertEqual(len(registry.commands), len(PORTED_COMMANDS))
+
+    def test_tool_count_matches_ported_tools(self) -> None:
+        registry = build_execution_registry()
+        self.assertEqual(len(registry.tools), len(PORTED_TOOLS))
+
+
+class TestCommandLookup(unittest.TestCase):
+    """Tests for ExecutionRegistry.command() lookup."""
+
+    def setUp(self) -> None:
+        self.registry = build_execution_registry()
+        self.known_name = self.registry.commands[0].name
+
+    def test_lookup_exact_case(self) -> None:
+        result = self.registry.command(self.known_name)
+        self.assertIsNotNone(result)
+        self.assertEqual(result.name, self.known_name)
+
+    def test_lookup_case_insensitive_lower(self) -> None:
+        result = self.registry.command(self.known_name.lower())
+        self.assertIsNotNone(result)
+        self.assertEqual(result.name, self.known_name)
+
+    def test_lookup_case_insensitive_upper(self) -> None:
+        result = self.registry.command(self.known_name.upper())
+        self.assertIsNotNone(result)
+        self.assertEqual(result.name, self.known_name)
+
+    def test_lookup_case_insensitive_mixed(self) -> None:
+        mixed = ''.join(
+            c.upper() if i % 2 else c.lower()
+            for i, c in enumerate(self.known_name)
+        )
+        result = self.registry.command(mixed)
+        self.assertIsNotNone(result)
+        self.assertEqual(result.name, self.known_name)
+
+    def test_returns_none_for_unknown_name(self) -> None:
+        result = self.registry.command('__nonexistent_command_xyz__')
+        self.assertIsNone(result)
+
+
+class TestToolLookup(unittest.TestCase):
+    """Tests for ExecutionRegistry.tool() lookup."""
+
+    def setUp(self) -> None:
+        self.registry = build_execution_registry()
+        self.known_name = self.registry.tools[0].name
+
+    def test_lookup_exact_case(self) -> None:
+        result = self.registry.tool(self.known_name)
+        self.assertIsNotNone(result)
+        self.assertEqual(result.name, self.known_name)
+
+    def test_lookup_case_insensitive_lower(self) -> None:
+        result = self.registry.tool(self.known_name.lower())
+        self.assertIsNotNone(result)
+        self.assertEqual(result.name, self.known_name)
+
+    def test_lookup_case_insensitive_upper(self) -> None:
+        result = self.registry.tool(self.known_name.upper())
+        self.assertIsNotNone(result)
+        self.assertEqual(result.name, self.known_name)
+
+    def test_lookup_case_insensitive_mixed(self) -> None:
+        mixed = ''.join(
+            c.upper() if i % 2 else c.lower()
+            for i, c in enumerate(self.known_name)
+        )
+        result = self.registry.tool(mixed)
+        self.assertIsNotNone(result)
+        self.assertEqual(result.name, self.known_name)
+
+    def test_returns_none_for_unknown_name(self) -> None:
+        result = self.registry.tool('__nonexistent_tool_xyz__')
+        self.assertIsNone(result)
+
+
+class TestMirroredCommand(unittest.TestCase):
+    """Tests for MirroredCommand dataclass."""
+
+    def test_has_correct_name(self) -> None:
+        cmd = MirroredCommand(name='review', source_hint='copilot')
+        self.assertEqual(cmd.name, 'review')
+
+    def test_has_correct_source_hint(self) -> None:
+        cmd = MirroredCommand(name='review', source_hint='copilot')
+        self.assertEqual(cmd.source_hint, 'copilot')
+
+    def test_is_frozen(self) -> None:
+        cmd = MirroredCommand(name='review', source_hint='copilot')
+        with self.assertRaises(AttributeError):
+            cmd.name = 'other'  # type: ignore[misc]
+
+    def test_execute_returns_string(self) -> None:
+        registry = build_execution_registry()
+        cmd = registry.commands[0]
+        result = cmd.execute('test prompt')
+        self.assertIsInstance(result, str)
+        self.assertIn('Mirrored command', result)
+
+
+class TestMirroredTool(unittest.TestCase):
+    """Tests for MirroredTool dataclass."""
+
+    def test_has_correct_name(self) -> None:
+        tool = MirroredTool(name='BashTool', source_hint='vscode')
+        self.assertEqual(tool.name, 'BashTool')
+
+    def test_has_correct_source_hint(self) -> None:
+        tool = MirroredTool(name='BashTool', source_hint='vscode')
+        self.assertEqual(tool.source_hint, 'vscode')
+
+    def test_is_frozen(self) -> None:
+        tool = MirroredTool(name='BashTool', source_hint='vscode')
+        with self.assertRaises(AttributeError):
+            tool.name = 'other'  # type: ignore[misc]
+
+    def test_execute_returns_string(self) -> None:
+        registry = build_execution_registry()
+        tool = registry.tools[0]
+        result = tool.execute('test payload')
+        self.assertIsInstance(result, str)
+        self.assertIn('Mirrored tool', result)
+
+
+class TestEmptyRegistry(unittest.TestCase):
+    """Tests for an empty ExecutionRegistry."""
+
+    def setUp(self) -> None:
+        self.registry = ExecutionRegistry(commands=(), tools=())
+
+    def test_command_returns_none(self) -> None:
+        self.assertIsNone(self.registry.command('anything'))
+
+    def test_tool_returns_none(self) -> None:
+        self.assertIsNone(self.registry.tool('anything'))
+
+    def test_empty_commands_tuple(self) -> None:
+        self.assertEqual(len(self.registry.commands), 0)
+
+    def test_empty_tools_tuple(self) -> None:
+        self.assertEqual(len(self.registry.tools), 0)
+
+
+if __name__ == '__main__':
+    unittest.main()