Add unit tests for hello_world LangGraph sample

- Test basic workflow execution with query processing
- Test empty query handling
- Add fixture to clear global registry between tests

Author: mfateev

tests/langgraph_samples/__init__.py

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+# LangGraph samples tests

tests/langgraph_samples/hello_world_test.py

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+"""Tests for the hello_world LangGraph sample."""
+
+import uuid
+
+import pytest
+from temporalio.client import Client
+from temporalio.contrib.langgraph import LangGraphPlugin
+from temporalio.contrib.langgraph._graph_registry import get_global_registry
+from temporalio.worker import Worker
+
+from langgraph_samples.hello_world.graph import build_hello_graph
+from langgraph_samples.hello_world.workflow import HelloWorldWorkflow
+
+
+@pytest.fixture(autouse=True)
+def clear_registry() -> None:
+    """Clear the global graph registry before each test."""
+    get_global_registry().clear()
+
+
+async def test_hello_world_workflow(client: Client) -> None:
+    """Test that the hello world workflow processes a query correctly."""
+    task_queue = f"hello-world-test-{uuid.uuid4()}"
+
+    # Create plugin with the graph
+    plugin = LangGraphPlugin(graphs={"hello_graph": build_hello_graph})
+
+    async with Worker(
+        client,
+        task_queue=task_queue,
+        workflows=[HelloWorldWorkflow],
+        plugins=[plugin],
+    ):
+        result = await client.execute_workflow(
+            HelloWorldWorkflow.run,
+            "Hello from test",
+            id=f"hello-world-{uuid.uuid4()}",
+            task_queue=task_queue,
+        )
+
+        assert result["result"] == "Processed: Hello from test"
+
+
+async def test_hello_world_empty_query(client: Client) -> None:
+    """Test hello world workflow with empty query."""
+    task_queue = f"hello-world-test-{uuid.uuid4()}"
+
+    plugin = LangGraphPlugin(graphs={"hello_graph": build_hello_graph})
+
+    async with Worker(
+        client,
+        task_queue=task_queue,
+        workflows=[HelloWorldWorkflow],
+        plugins=[plugin],
+    ):
+        result = await client.execute_workflow(
+            HelloWorldWorkflow.run,
+            "",
+            id=f"hello-world-{uuid.uuid4()}",
+            task_queue=task_queue,
+        )
+
+        assert result["result"] == "Processed: "