Add test verifying Slack messaging helpers

[haoruizhou]

Summary

• add a pytest that exercises send_slack_message and send_slack_image using a dummy Slack client
• generate a random scatter plot fixture to ensure image uploads include real file content

Testing

• pytest tests/test_slackbot_messaging.py

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Guard matplotlib dependency in new slackbot test

The new tests/test_slackbot_messaging.py imports matplotlib.pyplot unconditionally (line 6) even though the repository has no top-level dependency specification that installs Matplotlib for the test environment. Running pytest on a clean checkout now fails during collection with ModuleNotFoundError: No module named 'matplotlib', so the entire test suite is broken unless developers manually install extra packages. Please either add Matplotlib (and the other Slackbot dependencies) to the project’s dev/test requirements or skip this test when Matplotlib is unavailable so pytest can run out of the box.

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