chore: Make UT of a2a consistent about how tests should be skipped when python verison < 3.10

PiperOrigin-RevId: 801040421

tests/unittests/agents/test_langgraph_agent.py

@@ -14,17 +14,84 @@
 
 from unittest.mock import MagicMock
 
-from google.adk.agents.invocation_context import InvocationContext
-from google.adk.agents.langgraph_agent import LangGraphAgent
-from google.adk.events.event import Event
-from google.adk.plugins.plugin_manager import PluginManager
-from google.genai import types
-from langchain_core.messages import AIMessage
-from langchain_core.messages import HumanMessage
-from langchain_core.messages import SystemMessage
-from langgraph.graph.graph import CompiledGraph
 import pytest
 
+# Skip all tests in this module if LangGraph dependencies are not available
+LANGGRAPH_AVAILABLE = True
+try:
+  from google.adk.agents.invocation_context import InvocationContext
+  from google.adk.agents.langgraph_agent import LangGraphAgent
+  from google.adk.events.event import Event
+  from google.adk.plugins.plugin_manager import PluginManager
+  from google.genai import types
+  from langchain_core.messages import AIMessage
+  from langchain_core.messages import HumanMessage
+  from langchain_core.messages import SystemMessage
+  from langgraph.graph.graph import CompiledGraph
+except ImportError:
+  LANGGRAPH_AVAILABLE = False
+
+  # IMPORTANT: Dummy classes are REQUIRED in this file but NOT in A2A test files.
+  # Here's why this file is different from A2A test files:
+  #
+  # 1. MODULE-LEVEL USAGE IN DECORATORS:
+  #    This file uses @pytest.mark.parametrize decorator with complex nested structures
+  #    that directly reference imported types like Event(), types.Content(), types.Part.from_text().
+  #    These decorator expressions are evaluated during MODULE COMPILATION TIME,
+  #    not during test execution time.
+  #
+  # 2. A2A TEST FILES PATTERN:
+  #    Most A2A test files only use imported types within test method bodies:
+  #    - Inside test functions: def test_something(): Message(...)
+  #    - These are evaluated during TEST EXECUTION TIME when tests are skipped
+  #    - No NameError occurs because skipped tests don't execute their bodies
+  #
+  # 3. WHAT HAPPENS WITHOUT DUMMIES:
+  #    If we remove dummy classes from this file:
+  #    - Python tries to compile the @pytest.mark.parametrize decorator
+  #    - It encounters Event(...), types.Content(...), etc.
+  #    - These names are undefined → NameError during module compilation
+  #    - Test collection fails before pytest.mark.skipif can even run
+  #
+  # 4. WHY DUMMIES WORK:
+  #    - DummyTypes() can be called like Event() → returns DummyTypes instance
+  #    - DummyTypes.__getattr__ handles types.Content → returns DummyTypes instance
+  #    - DummyTypes.__call__ handles types.Part.from_text() → returns DummyTypes instance
+  #    - The parametrize decorator gets dummy objects instead of real ones
+  #    - Tests still get skipped due to pytestmark, so dummies never actually run
+  #
+  # 5. EXCEPTION CASES IN A2A FILES:
+  #    A few A2A files DID need dummies initially because they had:
+  #    - Type annotations: def create_helper(x: str) -> Message
+  #    - But we removed those type annotations to eliminate the need for dummies
+  #
+  # This file cannot avoid dummies because the parametrize decorator usage
+  # is fundamental to the test structure and cannot be easily refactored.
+
+  class DummyTypes:
+
+    def __getattr__(self, name):
+      return DummyTypes()
+
+    def __call__(self, *args, **kwargs):
+      return DummyTypes()
+
+  InvocationContext = DummyTypes()
+  LangGraphAgent = DummyTypes()
+  Event = DummyTypes()
+  PluginManager = DummyTypes()
+  types = (
+      DummyTypes()
+  )  # Must support chained calls like types.Content(), types.Part.from_text()
+  AIMessage = DummyTypes()
+  HumanMessage = DummyTypes()
+  SystemMessage = DummyTypes()
+  CompiledGraph = DummyTypes()
+
+pytestmark = pytest.mark.skipif(
+    not LANGGRAPH_AVAILABLE, reason="LangGraph dependencies not available"
+)
+
 
 @pytest.mark.parametrize(
     "checkpointer_value, events_list, expected_messages",