Task 4: Add Services & Utilities tests (66 tests)

- test_media_utils.py: 29 tests for check_media_files, get_media_file_paths,
  has_all_images, count_video_files, has_video_files, constants
- test_nfo_factory.py: 11 tests for NFOServiceFactory.create, create_optional,
  get_nfo_factory singleton, create_nfo_service convenience
- test_series_manager_service.py: 15 tests for init, from_settings,
  process_nfo_for_series, scan_and_process_nfo, close
- test_templates_utils.py: 4 tests for TEMPLATES_DIR path resolution
- test_error_controller.py: 7 tests for 404/500 handlers (API vs HTML)

tests/unit/test_error_controller.py

@@ -0,0 +1,110 @@
+"""Unit tests for error controller module.
+
+Tests custom 404 and 500 error handlers for both API and HTML responses.
+"""
+
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+from fastapi import HTTPException, Request
+
+from src.server.controllers.error_controller import (
+    not_found_handler,
+    server_error_handler,
+)
+
+
+def _make_request(path: str = "/") -> MagicMock:
+    """Create a mock Request object with a given path."""
+    request = MagicMock(spec=Request)
+    url = MagicMock()
+    url.path = path
+    request.url = url
+    return request
+
+
+class TestNotFoundHandler:
+    """Tests for the 404 not_found_handler."""
+
+    @pytest.mark.asyncio
+    async def test_api_path_returns_json(self):
+        """API paths get a JSON response with 404 status."""
+        request = _make_request("/api/anime/123")
+        exc = HTTPException(status_code=404)
+        resp = await not_found_handler(request, exc)
+        assert resp.status_code == 404
+        assert resp.body is not None
+
+    @pytest.mark.asyncio
+    @patch("src.server.controllers.error_controller.render_template")
+    async def test_web_path_renders_template(self, mock_render):
+        """Non-API paths render the error template."""
+        mock_render.return_value = MagicMock(status_code=404)
+        request = _make_request("/anime/details")
+        exc = HTTPException(status_code=404)
+        await not_found_handler(request, exc)
+        mock_render.assert_called_once_with(
+            "error.html",
+            request,
+            context={"error": "Page not found", "status_code": 404},
+            title="404 - Not Found",
+        )
+
+    @pytest.mark.asyncio
+    async def test_api_json_structure(self):
+        """API 404 response has 'detail' field."""
+        import json
+        request = _make_request("/api/missing")
+        exc = HTTPException(status_code=404)
+        resp = await not_found_handler(request, exc)
+        body = json.loads(resp.body)
+        assert body["detail"] == "API endpoint not found"
+
+
+class TestServerErrorHandler:
+    """Tests for the 500 server_error_handler."""
+
+    @pytest.mark.asyncio
+    async def test_api_path_returns_json(self):
+        """API paths get a JSON response with 500 status."""
+        request = _make_request("/api/download")
+        exc = RuntimeError("crash")
+        resp = await server_error_handler(request, exc)
+        assert resp.status_code == 500
+
+    @pytest.mark.asyncio
+    @patch("src.server.controllers.error_controller.render_template")
+    async def test_web_path_renders_template(self, mock_render):
+        """Non-API paths render the error template."""
+        mock_render.return_value = MagicMock(status_code=500)
+        request = _make_request("/settings")
+        exc = RuntimeError("crash")
+        await server_error_handler(request, exc)
+        mock_render.assert_called_once_with(
+            "error.html",
+            request,
+            context={"error": "Internal server error", "status_code": 500},
+            title="500 - Server Error",
+        )
+
+    @pytest.mark.asyncio
+    async def test_api_error_does_not_expose_stack_trace(self):
+        """API 500 response doesn't contain the actual error message."""
+        import json
+        request = _make_request("/api/vulnerable")
+        exc = RuntimeError("secret database credentials")
+        resp = await server_error_handler(request, exc)
+        body = json.loads(resp.body)
+        assert "secret" not in body["detail"]
+        assert body["detail"] == "Internal server error"
+
+    @pytest.mark.asyncio
+    async def test_api_path_detection(self):
+        """Correctly distinguishes API vs web paths."""
+        api_request = _make_request("/api/test")
+        web_request = _make_request("/dashboard")
+
+        # API path returns JSONResponse
+        from fastapi.responses import JSONResponse
+        resp = await server_error_handler(api_request, Exception("err"))
+        assert isinstance(resp, JSONResponse)