Fix fastloop initialization and add regression test (#16)

* Fix: Improve app path inference and add regression tests

Co-authored-by: luke <luke@smartshare.io>

* Refactor tests and improve app initialization logic

Co-authored-by: luke <luke@smartshare.io>

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

Author: luke-lombardi

fastloop/utils.py

@@ -58,13 +58,16 @@ def infer_application_path(app_instance: Any, fallback_var: str = "app") -> str
         Application path string like "module.path:app" or None if cannot be determined
     """
     # (1) Introspect app if it has an 'app' attribute (e.g., FastLoop wrapping FastAPI)
-    app = getattr(app_instance, "app", None) or app_instance
+    # Note: We don't fall back to app_instance here because app_instance.__module__
+    # would be "fastloop.fastloop" (where the class is defined), not the user's module.
+    # If there's no 'app' attribute, we fall through to argv-based inference.
+    app = getattr(app_instance, "app", None)
     if app is not None and getattr(app, "__module__", None):
         mod_name = app.__module__
         try:
             mod = importlib.import_module(mod_name)
             for name, val in vars(mod).items():
-                if val is app or val is app_instance:
+                if val is app:
                     return f"{mod_name}:{name}"
             # app object found but variable name not recoverable — use fallback var
             return f"{mod_name}:{fallback_var}"

tests/test_app_initialization.py

@@ -0,0 +1,169 @@
+"""
+Regression tests for FastLoop app initialization.
+
+These tests ensure that:
+1. The application path inference works correctly for hypercorn hot reload
+2. FastLoop apps with registered loops initialize properly
+
+Regression for: When infer_application_path incorrectly returns "fastloop.fastloop:app",
+hypercorn fails with:
+    NoAppError: Cannot load application from 'fastloop.fastloop:app', application not found.
+"""
+
+import sys
+import tempfile
+from pathlib import Path
+from unittest import mock
+
+from fastloop import FastLoop
+from fastloop.context import LoopContext
+from fastloop.loop import LoopEvent
+from fastloop.utils import infer_application_path
+
+# --- Event Types for Testing ---
+
+
+class QueryEvent(LoopEvent):
+    type: str = "query"
+    message: str
+
+
+class ResponseEvent(LoopEvent):
+    type: str = "response"
+    reply: str
+
+
+# --- Test Classes ---
+
+
+class TestInferApplicationPath:
+    """
+    Regression tests for infer_application_path.
+
+    The bug: When a FastLoop instance has no 'app' attribute, the function
+    was falling back to app_instance itself, returning "fastloop.fastloop:app"
+    which doesn't exist.
+    """
+
+    def test_does_not_return_fastloop_module_path(self):
+        """FastLoop instances should NOT resolve to the fastloop package."""
+        app = FastLoop(name="test-app")
+        result = infer_application_path(app)
+
+        if result is not None:
+            assert not result.startswith("fastloop."), (
+                f"infer_application_path returned '{result}' pointing to fastloop package. "
+                "This causes: NoAppError: Cannot load application from 'fastloop.fastloop:app'"
+            )
+
+    def test_falls_back_to_argv_inference(self):
+        """When no module var found, should use argv-based inference."""
+        app = FastLoop(name="test-app")
+
+        with tempfile.TemporaryDirectory() as tmpdir:
+            script_path = Path(tmpdir) / "myapp" / "main.py"
+            script_path.parent.mkdir(parents=True)
+            script_path.touch()
+
+            with (
+                mock.patch.object(sys, "argv", [str(script_path)]),
+                mock.patch.object(sys, "path", [tmpdir, *sys.path]),
+            ):
+                result = infer_application_path(app)
+
+                if result is not None:
+                    assert "myapp.main" in result
+                    assert ":app" in result
+
+
+class TestFastLoopWithLoops:
+    """Tests for FastLoop app with registered loops."""
+
+    def test_app_with_loop_decorator(self):
+        """
+        Test that a FastLoop app with a @loop decorator initializes correctly
+        and doesn't cause import issues.
+        """
+        app = FastLoop(name="test-chat-app")
+        app.register_events([QueryEvent, ResponseEvent])
+
+        async def on_start(context: LoopContext):
+            await context.set("initialized", True)
+
+        @app.loop("chat", start_event=QueryEvent, on_start=on_start)
+        async def chat_loop(context: LoopContext):
+            msg = await context.wait_for(QueryEvent, raise_on_timeout=False, timeout=1)
+            if msg is None:
+                return
+            await context.emit(ResponseEvent(reply=f"Echo: {msg.message}"))
+
+        # Verify loop was registered
+        assert "chat" in app._loop_metadata
+        assert app._loop_metadata["chat"]["func"] == chat_loop
+        assert app._loop_metadata["chat"]["start_event"] == "query"
+
+        # Verify events were registered
+        assert "query" in app._event_types
+        assert "response" in app._event_types
+
+        # Verify infer_application_path doesn't break
+        result = infer_application_path(app)
+        if result is not None:
+            assert not result.startswith("fastloop.")
+
+    def test_app_with_multiple_loops(self):
+        """Test app with multiple loop definitions."""
+        app = FastLoop(name="multi-loop-app")
+        app.register_events([QueryEvent, ResponseEvent])
+
+        @app.loop("loop-a", start_event=QueryEvent)
+        async def loop_a(context: LoopContext):
+            pass
+
+        @app.loop("loop-b", start_event=ResponseEvent)
+        async def loop_b(context: LoopContext):
+            pass
+
+        assert "loop-a" in app._loop_metadata
+        assert "loop-b" in app._loop_metadata
+        assert len(app._loop_metadata) == 2
+
+    def test_app_routes_registered(self):
+        """Verify that loop decorator registers the expected API routes."""
+        app = FastLoop(name="route-test-app")
+        app.register_events([QueryEvent])
+
+        @app.loop("myloop", start_event=QueryEvent)
+        async def my_loop(context: LoopContext):
+            pass
+
+        # Check routes were added
+        route_paths = [route.path for route in app.routes]
+        assert "/myloop" in route_paths
+        assert "/myloop/{loop_id}" in route_paths
+        assert "/myloop/{loop_id}/stop" in route_paths
+        assert "/myloop/{loop_id}/pause" in route_paths
+
+
+class TestAppConfiguration:
+    """Tests for FastLoop configuration."""
+
+    def test_debug_mode_defaults_to_false(self):
+        """Debug mode should be off by default."""
+        app = FastLoop(name="test-app")
+        assert app.config_manager.get("debugMode", False) is False
+
+    def test_custom_config_applied(self):
+        """Custom config should be merged with defaults."""
+        app = FastLoop(
+            name="test-app",
+            config={"port": 9000, "debugMode": True},
+        )
+        assert app.config_manager.get("port") == 9000
+        assert app.config_manager.get("debugMode") is True
+
+    def test_fastloop_has_no_app_attribute(self):
+        """FastLoop should not have an 'app' attribute (it IS the app)."""
+        app = FastLoop(name="test-app")
+        # FastLoop is a FastAPI subclass, not a wrapper
+        assert getattr(app, "app", None) is None