feat: Implement PluginService for registering and executing plugins

PluginService takes the registration of plugins, and provide the wrapper utilities to execute all plugins.

PiperOrigin-RevId: 769834609

Author: pwwpche

tests/unittests/plugins/test_base_plugin.py

@@ -0,0 +1,239 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import annotations
+
+from unittest.mock import Mock
+
+from google.adk.agents.base_agent import BaseAgent
+from google.adk.agents.callback_context import CallbackContext
+from google.adk.agents.invocation_context import InvocationContext
+from google.adk.events.event import Event
+from google.adk.models.llm_request import LlmRequest
+from google.adk.models.llm_response import LlmResponse
+from google.adk.plugins.base_plugin import BasePlugin
+from google.adk.tools.base_tool import BaseTool
+from google.adk.tools.tool_context import ToolContext
+from google.genai import types
+import pytest
+
+
+class TestablePlugin(BasePlugin):
+  __test__ = False
+  """A concrete implementation of BasePlugin for testing purposes."""
+  pass
+
+
+class FullOverridePlugin(BasePlugin):
+  __test__ = False
+
+  """A plugin that overrides every single callback method for testing."""
+
+  def __init__(self, name: str = "full_override"):
+    super().__init__(name)
+
+  async def on_user_message_callback(self, **kwargs) -> str:
+    return "overridden_on_user_message"
+
+  async def before_run_callback(self, **kwargs) -> str:
+    return "overridden_before_run"
+
+  async def after_run_callback(self, **kwargs) -> str:
+    return "overridden_after_run"
+
+  async def on_event_callback(self, **kwargs) -> str:
+    return "overridden_on_event"
+
+  async def before_agent_callback(self, **kwargs) -> str:
+    return "overridden_before_agent"
+
+  async def after_agent_callback(self, **kwargs) -> str:
+    return "overridden_after_agent"
+
+  async def before_tool_callback(self, **kwargs) -> str:
+    return "overridden_before_tool"
+
+  async def after_tool_callback(self, **kwargs) -> str:
+    return "overridden_after_tool"
+
+  async def before_model_callback(self, **kwargs) -> str:
+    return "overridden_before_model"
+
+  async def after_model_callback(self, **kwargs) -> str:
+    return "overridden_after_model"
+
+
+def test_base_plugin_initialization():
+  """Tests that a plugin is initialized with the correct name."""
+  plugin_name = "my_test_plugin"
+  plugin = TestablePlugin(name=plugin_name)
+  assert plugin.name == plugin_name
+
+
+@pytest.mark.asyncio
+async def test_base_plugin_default_callbacks_return_none():
+  """Tests that the default (non-overridden) callbacks in BasePlugin exist
+
+  and return None as expected.
+  """
+  plugin = TestablePlugin(name="default_plugin")
+
+  # Mocking all necessary context objects
+  mock_context = Mock()
+  mock_user_message = Mock()
+
+  # The default implementations should do nothing and return None.
+  assert (
+      await plugin.on_user_message_callback(
+          user_message=mock_user_message,
+          invocation_context=mock_context,
+      )
+      is None
+  )
+  assert (
+      await plugin.before_run_callback(invocation_context=mock_context) is None
+  )
+  assert (
+      await plugin.after_run_callback(invocation_context=mock_context) is None
+  )
+  assert (
+      await plugin.on_event_callback(
+          invocation_context=mock_context, event=mock_context
+      )
+      is None
+  )
+  assert (
+      await plugin.before_agent_callback(
+          agent=mock_context, callback_context=mock_context
+      )
+      is None
+  )
+  assert (
+      await plugin.after_agent_callback(
+          agent=mock_context, callback_context=mock_context
+      )
+      is None
+  )
+  assert (
+      await plugin.before_tool_callback(
+          tool=mock_context, tool_args={}, tool_context=mock_context
+      )
+      is None
+  )
+  assert (
+      await plugin.after_tool_callback(
+          tool=mock_context, tool_args={}, tool_context=mock_context, result={}
+      )
+      is None
+  )
+  assert (
+      await plugin.before_model_callback(
+          callback_context=mock_context, llm_request=mock_context
+      )
+      is None
+  )
+  assert (
+      await plugin.after_model_callback(
+          callback_context=mock_context, llm_response=mock_context
+      )
+      is None
+  )
+
+
+@pytest.mark.asyncio
+async def test_base_plugin_all_callbacks_can_be_overridden():
+  """Verifies that a user can create a subclass of BasePlugin and that all
+
+  overridden methods are correctly called.
+  """
+  plugin = FullOverridePlugin()
+
+  # Create mock objects for all required arguments. We don't need real
+  # objects, just placeholders to satisfy the method signatures.
+  mock_user_message = Mock(spec=types.Content)
+  mock_invocation_context = Mock(spec=InvocationContext)
+  mock_callback_context = Mock(spec=CallbackContext)
+  mock_agent = Mock(spec=BaseAgent)
+  mock_tool = Mock(spec=BaseTool)
+  mock_tool_context = Mock(spec=ToolContext)
+  mock_llm_request = Mock(spec=LlmRequest)
+  mock_llm_response = Mock(spec=LlmResponse)
+  mock_event = Mock(spec=Event)
+
+  # Call each method and assert it returns the unique string from the override.
+  # This proves that the subclass's method was executed.
+  assert (
+      await plugin.on_user_message_callback(
+          user_message=mock_user_message,
+          invocation_context=mock_invocation_context,
+      )
+      == "overridden_on_user_message"
+  )
+  assert (
+      await plugin.before_run_callback(
+          invocation_context=mock_invocation_context
+      )
+      == "overridden_before_run"
+  )
+  assert (
+      await plugin.after_run_callback(
+          invocation_context=mock_invocation_context
+      )
+      == "overridden_after_run"
+  )
+  assert (
+      await plugin.on_event_callback(
+          invocation_context=mock_invocation_context, event=mock_event
+      )
+      == "overridden_on_event"
+  )
+  assert (
+      await plugin.before_agent_callback(
+          agent=mock_agent, callback_context=mock_callback_context
+      )
+      == "overridden_before_agent"
+  )
+  assert (
+      await plugin.after_agent_callback(
+          agent=mock_agent, callback_context=mock_callback_context
+      )
+      == "overridden_after_agent"
+  )
+  assert (
+      await plugin.before_model_callback(
+          callback_context=mock_callback_context, llm_request=mock_llm_request
+      )
+      == "overridden_before_model"
+  )
+  assert (
+      await plugin.after_model_callback(
+          callback_context=mock_callback_context, llm_response=mock_llm_response
+      )
+      == "overridden_after_model"
+  )
+  assert (
+      await plugin.before_tool_callback(
+          tool=mock_tool, tool_args={}, tool_context=mock_tool_context
+      )
+      == "overridden_before_tool"
+  )
+  assert (
+      await plugin.after_tool_callback(
+          tool=mock_tool,
+          tool_args={},
+          tool_context=mock_tool_context,
+          result={},
+      )
+      == "overridden_after_tool"
+  )