[python-package] Add tests for some plotting functions

[DeborahOlaboye]

Contributes to #7031 by expanding test coverage for plotting module parameters.

New tests added:

Item from #7031	Function	Parameter
✅	plot_importance()	max_num_features
✅	plot_split_value_histogram()	xlim
✅	plot_metric()	xlim

Test plan

• pytest tests/python_package_test/test_plotting.py::test_plot_importance passes
• pytest tests/python_package_test/test_plotting.py::test_plot_split_value_histogram passes
• pytest tests/python_package_test/test_plotting.py::test_plot_metrics passes

[DeborahOlaboye]

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[jameslamb]

Please revert all the unrelated formatting changes you made in this PR, and the test cases on ylim and figsize that are already being handled in #7142 and #7143 .

When you do that, please also update your branch to the latest master.

After that, we'll be happy to review again.

[DeborahOlaboye]

Please revert all the unrelated formatting changes you made in this PR, and the test cases on ylim and figsize that are already being handled in #7142 and #7143 .

When you do that, please also update your branch to the latest master.

After that, we'll be happy to review again.

Alright, all unrelated formatting changes has been reverted and branch updated to the latest master. Thank you.

[jameslamb]

Thanks for working on this! I left some suggestions for making these tests a bit stronger.

[jameslamb]

I've updated the description and title, removing references to tests that you've since removed.

It would be ok to add back ylim and figsize tests for functions that are not plot_importance() if you'd like... all I meant in #7144 (review) is that those other PRs were already adding tests on plot_importance(). You could also do this in a follow-up PR, whichever you'd like.

[DeborahOlaboye]

I've updated the description and title, removing references to tests that you've since removed.

It would be ok to add back ylim and figsize tests for functions that are not plot_importance() if you'd like... all I meant in #7144 (review) is that those other PRs were already adding tests on plot_importance(). You could also do this in a follow-up PR, whichever you'd like.

Thanks for clarifying and for updating the title. I'll add ylim and figsize tests for plot_metric() and plot_split_value_histogram() in a follow-up PR.