test(cli): refactor test_components_path to use async thread and free port (#8748)

* Refactor test_components_path to run server in thread

The test now starts the CLI server in a separate thread on a free port, allowing asynchronous startup and avoiding port conflicts. This change improves test reliability and better simulates real server behavior.

* Update src/backend/tests/unit/test_cli.py

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* Improve error handling in run_flow CLI test helper

The run_flow function now raises a RuntimeError with a detailed message if the CLI invocation fails, making test failures easier to diagnose.

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

src/backend/tests/unit/test_cli.py

@@ -1,3 +1,7 @@
+import socket
+import threading
+import time
+
 import pytest
 from langflow.__main__ import app
 from langflow.services import deps
@@ -11,16 +15,44 @@ def default_settings():
     ]
 
 
+def get_free_port():
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+        s.bind(("", 0))
+        return s.getsockname()[1]
+
+
+def run_flow(runner, port, components_path, default_settings):
+    args = [
+        "run",
+        "--port",
+        str(port),
+        "--components-path",
+        str(components_path),
+        *default_settings,
+    ]
+    result = runner.invoke(app, args)
+    if result.exit_code != 0:
+        msg = f"CLI failed with exit code {result.exit_code}: {result.output}"
+        raise RuntimeError(msg)
+
+
 def test_components_path(runner, default_settings, tmp_path):
     # create a "components" folder
     temp_dir = tmp_path / "components"
     temp_dir.mkdir(exist_ok=True)
 
-    result = runner.invoke(
-        app,
-        ["run", "--components-path", str(temp_dir), *default_settings],
+    port = get_free_port()
+
+    thread = threading.Thread(
+        target=run_flow,
+        args=(runner, port, temp_dir, default_settings),
+        daemon=True,
     )
-    assert result.exit_code == 0, result.stdout
+    thread.start()
+
+    # Give the server some time to start
+    time.sleep(5)
+
     settings_service = deps.get_settings_service()
     assert str(temp_dir) in settings_service.settings.components_path