Add test_contour under test_datetime.py

[kots14]

PR summary

Attempting adding code for test_contour method in test_datetime.py mentioned in #26864

Image output -

PR checklist

• resolves #26864
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines

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[ksunden]

Having 6 instead of 3 plots is slightly unnecessary (Z does not actually go through units behavior, and both Z values are just floats anyway)

But it looks correct and is testing what we want to test here.

Thank you @kots14

[kots14]

@ksunden Thank you for your feedback and for approving the changes.
In order to get this PR merged, is there any further modification expected?

[QuLogic]

I suppose the extra 3 Axes could be removed if you're making updates.

[kots14]

I suppose the extra 3 Axes could be removed if you're making updates.

You mean from these lines shall I remove 3?

ax1.contour(X_dates, Y_dates, Z_timestamps)
ax2.contour(X_dates, Y_ranges, Z_timestamps)
ax3.contour(X_ranges, Y_dates, Z_timestamps)
bx1.contour(X_dates, Y_dates, Z_ranges)
bx2.contour(X_dates, Y_ranges, Z_ranges)
bx3.contour(X_ranges, Y_dates, Z_ranges)

[ksunden]

The last three (and get rid of the variables that become unused as a result).

[QuLogic]

Thanks @kots14! Congratulations on your first PR to Matplotlib 🎉 We hope to hear from you again.