Fix CI abort: skip PyVista Plotter test on headless runners

[lmoresi]

Summary

• test_pyvista_plotter_available creates a pv.Plotter(off_screen=True) which calls VTK's OpenGL probe — this aborts the entire process on headless GitHub Actions runners (no DISPLAY). The abort kills the test_08* pytest session (334 tests), masking all results from that batch.
• Added HAS_DISPLAY check using DISPLAY, WAYLAND_DISPLAY, or PYVISTA_OFF_SCREEN environment variables. Plotter tests skip when no display is available.
• Fixed \*\*kwargs escape sequences in model.py and materials.py docstrings (Python 3.12+ SyntaxWarning).

Test plan

• test_0800_optional_modules.py passes locally (10 passed, 4 skipped)
• Plotter test correctly skipped when no display available
• Docstring escape warnings eliminated
• CI should now pass all 334 tests in the test_08* batch (instead of aborting)

Underworld development team with AI support from Claude Code

[Copilot]

Pull request overview

This PR fixes a CI abort issue where test_pyvista_plotter_available was calling pv.Plotter(off_screen=True), which triggers VTK's OpenGL probe on headless GitHub Actions runners (no DISPLAY), causing a process abort that killed the entire test_08* pytest session. The fix introduces a display availability check and a new requires_pyvista_rendering skip marker, so the Plotter test is skipped on headless runners. The PR also fixes Python 3.12+ SyntaxWarning caused by unescaped \*\* in docstrings in model.py and materials.py.

Changes:

• Added HAS_DISPLAY / HAS_PYVISTA_RENDERING flags and a requires_pyvista_rendering skip marker based on display environment variable detection
• Switched test_pyvista_plotter_available from @requires_pyvista to @requires_pyvista_rendering and added a global pv.OFF_SCREEN = True assignment
• Fixed \*\*kwargs and \*args docstring escape sequences in model.py and materials.py

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
tests/test_0800_optional_modules.py	Adds display detection logic and requires_pyvista_rendering marker; updates Plotter test to skip on headless CI
src/underworld3/model.py	Fixes \*\*kwargs escape sequences in three docstrings to resolve Python 3.12+ SyntaxWarnings
src/underworld3/materials.py	Fixes \*args escape sequence in one docstring

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[Copilot]

Setting pv.OFF_SCREEN = True as a global module-level attribute mutation inside a test method has a side effect: it permanently modifies the PyVista global state for the entire test session. Any subsequent tests that create a pv.Plotter() without off_screen=True will inherit this global flag. Since this test already passes off_screen=True directly to pv.Plotter(), the global pv.OFF_SCREEN = True assignment is redundant and should be removed to avoid unintended side effects on other tests.

Suggested change

pv.OFF_SCREEN = True

[Copilot]

The skip reason at line 112 mentions only DISPLAY and PYVISTA_OFF_SCREEN, but the HAS_DISPLAY check at line 58-59 also includes WAYLAND_DISPLAY. The reason message should mention all three environment variables to give users accurate guidance on how to enable the test.

Suggested change

	reason="Requires pyvista and a display server (DISPLAY or PYVISTA_OFF_SCREEN)"
	reason="Requires pyvista and a display server (DISPLAY, WAYLAND_DISPLAY, or PYVISTA_OFF_SCREEN)"

[Copilot]

The import os statement is placed mid-file at line 57, after module-level dependency flags have already been set. The existing imports at the top of the file (lines 22-25) are where os should be imported along with pytest and sys. Placing imports mid-module deviates from PEP 8 conventions and from the import pattern used throughout this file. Move import os to the top-level imports block near line 22-24, alongside import pytest and import sys. Note that os is also re-imported inside check_petsc_has_pragmatic() at line 70, which would then be unnecessary.