feat(agent_toolkits): Make WebClient injectable for Slack toolkit (#145)

This PR enables injecting a
[`WebClient`](https://tools.slack.dev/python-slack-sdk/api-docs/slack_sdk/web/client.html)
instance into all tools within the Slack toolkit. This simplifies usage
for agents that need to work with [user
tokens](https://api.slack.com/concepts/token-types#user).

---------

Co-authored-by: Mason Daugherty <[email protected]>

Author: m1kl0sh

libs/community/langchain_community/agent_toolkits/slack/toolkit.py

@@ -46,8 +46,14 @@ class SlackToolkit(BaseToolkit):
 
             from langchain_community.agent_toolkits import SlackToolkit
 
+            # Using environment variables (default)
             toolkit = SlackToolkit()
 
+            # Or with an existing WebClient instance
+            from slack_sdk import WebClient
+            client = WebClient(token="your-user-token")
+            toolkit = SlackToolkit(client=client)
+
     Tools:
         .. code-block:: python
 
@@ -105,8 +111,8 @@ class SlackToolkit(BaseToolkit):
     def get_tools(self) -> List[BaseTool]:
         """Get the tools in the toolkit."""
         return [
-            SlackGetChannel(),
-            SlackGetMessage(),
-            SlackScheduleMessage(),
-            SlackSendMessage(),
+            SlackGetChannel(client=self.client),
+            SlackGetMessage(client=self.client),
+            SlackScheduleMessage(client=self.client),
+            SlackSendMessage(client=self.client),
         ]

libs/community/tests/unit_tests/agent_toolkits/test_slack_toolkit.py

@@ -0,0 +1,62 @@
+import sys
+from unittest.mock import MagicMock
+
+import pytest
+
+# Mock slack_sdk module and WebClient class.
+mock_slack_sdk = MagicMock()
+mock_webclient_class = MagicMock()
+mock_slack_sdk.WebClient = mock_webclient_class
+sys.modules["slack_sdk"] = mock_slack_sdk
+
+# We need to import the toolkit after patching sys.modules.
+# ruff: noqa: E402
+from langchain_community.agent_toolkits.slack.toolkit import SlackToolkit
+from langchain_community.tools.slack.base import SlackBaseTool
+
+
+@pytest.fixture
+def mock_webclient() -> MagicMock:
+    mock_client = MagicMock()
+    mock_client.api_test.return_value = {"ok": True}
+    return mock_client
+
+
+def test_slack_toolkit_default_instantiation() -> None:
+    """Test SlackToolkit can be instantiated with default settings."""
+    toolkit = SlackToolkit()
+    assert toolkit is not None
+
+    tools = toolkit.get_tools()
+
+    assert len(tools) == 4
+    for tool in tools:
+        assert isinstance(tool, SlackBaseTool)
+        assert tool.client == toolkit.client
+
+
+def test_slack_toolkit_get_tools_provided_client(mock_webclient: MagicMock) -> None:
+    """Test that get_tools() creates tools with the provided client."""
+    toolkit = SlackToolkit(client=mock_webclient)
+
+    tools = toolkit.get_tools()
+
+    assert len(tools) == 4
+    for tool in tools:
+        assert isinstance(tool, SlackBaseTool)
+        assert tool.client == mock_webclient
+
+
+def test_slack_toolkit_provided_client_reuse(mock_webclient: MagicMock) -> None:
+    """Test that provided client instance is reused across multiple get_tools()
+    calls."""
+    toolkit = SlackToolkit(client=mock_webclient)
+    tools1 = toolkit.get_tools()
+    tools2 = toolkit.get_tools()
+
+    for i in range(len(tools1)):
+        tool1 = tools1[i]
+        tool2 = tools2[i]
+        assert isinstance(tool1, SlackBaseTool)
+        assert isinstance(tool2, SlackBaseTool)
+        assert tool1.client == tool2.client == mock_webclient