tests: optimize test durations and refactor test fixtures (#3713)

* Refactor test fixtures and imports for optimization

- Reordered and optimized imports in `conftest.py`.
- Changed return statements to yield in `basic_graph` and `create_webhook` fixtures for better resource management.
- Added cleanup step to `create_webhook` fixture to delete created webhook after test completion.

* Refactor imports and add placeholder client fixture in test_ChatOllama_component.py

* Add pytest fixture 'client' to test_graph.py

* Add pytest fixture 'client' to test_callback_graph.py for test optimization

* Add 'unit_tests_looponfail' target to Makefile for running unit tests with loop-on-fail option

* Optimize test durations and update test cases in various modules

src/backend/tests/unit/components/models/test_ChatOllama_component.py

@@ -1,9 +1,16 @@
-import pytest
-from unittest.mock import patch, MagicMock
-from langflow.components.models.OllamaModel import ChatOllamaComponent
-from langchain_community.chat_models.ollama import ChatOllama
+from unittest.mock import MagicMock, patch
 from urllib.parse import urljoin
 
+import pytest
+from langchain_community.chat_models.ollama import ChatOllama
+
+from langflow.components.models.OllamaModel import ChatOllamaComponent
+
+
+@pytest.fixture
+def client():
+    pass
+
 
 @pytest.fixture
 def component():

src/backend/tests/unit/graph/graph/test_callback_graph.py

@@ -1,5 +1,7 @@
 import asyncio
 
+import pytest
+
 from langflow.components.outputs.ChatOutput import ChatOutput
 from langflow.custom.custom_component.component import Component
 from langflow.events.event_manager import EventManager
@@ -9,6 +11,11 @@ from langflow.schema.message import Message
 from langflow.template.field.base import Output
 
 
+@pytest.fixture
+def client():
+    pass
+
+
 class LogComponent(Component):
     name = "LogComponent"
     inputs = [IntInput(name="times", value=1)]

src/backend/tests/unit/graph/test_graph.py

@@ -25,6 +25,11 @@ from langflow.utils.payload import get_root_vertex
 # BASIC_EXAMPLE_PATH, COMPLEX_EXAMPLE_PATH, OPENAPI_EXAMPLE_PATH
 
 
+@pytest.fixture
+def client():
+    pass
+
+
 @pytest.fixture
 def sample_template():
     return {