fix(testing): subprocess client raises exc when fails to start (#4153)

bug(testing): subprocess client raises exc when fails to start (#4021)

Author: mmev

litestar/testing/client/subprocess_client.py

@@ -25,8 +25,18 @@ def _get_available_port() -> int:
 
 
 @contextmanager
-def run_app(workdir: pathlib.Path, app: str) -> Iterator[str]:
-    """Launch a litestar application in a subprocess with a random available port."""
+def run_app(workdir: pathlib.Path, app: str, retry_count: int = 100, retry_timeout: int = 1) -> Iterator[str]:
+    """Launch a litestar application in a subprocess with a random available port.
+
+    Args:
+        workdir: Path to working directory where run command will be executed
+        app: Path to Litestar application, e.g.: "my_app:application"
+        retry_count: Number of retries to wait for the application to start
+        retry_timeout: Timeout in seconds to wait between retries
+
+    Raises:
+        StartupError: If the application fails to start with given retry count and timeout
+    """
     port = _get_available_port()
     with subprocess.Popen(
         args=["litestar", "--app", app, "run", "--port", str(port)],
@@ -35,12 +45,20 @@ def run_app(workdir: pathlib.Path, app: str) -> Iterator[str]:
         cwd=workdir,
     ) as proc:
         url = f"http://127.0.0.1:{port}"
-        for _ in range(100):  # pragma: no cover
+        application_started = False
+
+        for _ in range(retry_count):
             try:
                 httpx.get(url, timeout=0.1)
+                application_started = True
                 break
             except httpx.TransportError:
-                time.sleep(1)
+                time.sleep(retry_timeout)
+
+        if not application_started:
+            proc.kill()
+            raise StartupError("Application failed to start")
+
         yield url
         proc.kill()
 

tests/unit/test_testing/test_sub_client/test_subprocess_client.py

@@ -12,25 +12,44 @@
 import pytest
 
 from litestar.testing import subprocess_async_client, subprocess_sync_client
+from litestar.testing.client.subprocess_client import StartupError, run_app
 
 if sys.platform == "win32":
     asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
 
 ROOT = pathlib.Path(__file__).parent
+APP = "demo:app"
 
 
 @pytest.fixture(name="async_client")
 async def fx_async_client() -> AsyncIterator[httpx.AsyncClient]:
-    async with subprocess_async_client(workdir=ROOT, app="demo:app") as client:
+    async with subprocess_async_client(workdir=ROOT, app=APP) as client:
         yield client
 
 
 @pytest.fixture(name="sync_client")
 def fx_sync_client() -> Iterator[httpx.Client]:
-    with subprocess_sync_client(workdir=ROOT, app="demo:app") as client:
+    with subprocess_sync_client(workdir=ROOT, app=APP) as client:
         yield client
 
 
+async def test_run_app() -> None:
+    """Ensure that method returns application url if started successfully"""
+    with run_app(workdir=ROOT, app=APP) as url:
+        assert isinstance(url, str)
+        assert url.startswith("http://127.0.0.1:")
+
+
+async def test_run_app_exception() -> None:
+    """
+    Ensure that method throws a StartupError if the application fails to start.
+    To simulate this, we set retry_count=0, so that we don't check if the application has started.
+    """
+    with pytest.raises(StartupError):
+        with run_app(workdir=ROOT, app=APP, retry_count=0):
+            ...
+
+
 async def test_subprocess_async_client(async_client: httpx.AsyncClient) -> None:
     """Demonstrates functionality of the async client with an infinite SSE source that cannot be tested with the
     regular async test client.