test(mobile): pin the behaviour of the plot style arguments

[petercorke]

What

Headless (Agg) tests of the Matplotlib style arguments of the planner, PRM and EKF plotting methods in roboticstoolbox.mobile. They pin down what each argument does today, so that the planned renaming (<thing>_style, old names deprecated, petercorke/rvc-ecosystem#15) and the merging of user styles over defaults can be made safely.

Coverage

• planner path styles (line, line_r), start and goal markers, and that a user's dict currently replaces the defaults rather than merging
• PRM vertex and edge styles, and that the dicts passed are not modified
• EKF.plot_xy (format string and keywords), plot_map (marker, ellipse) and plot_ellipse

Two expected failures

They record defects found while writing the tests; each flips to a failure when the defect is fixed, which is the cue to remove the marker.

• PlannerBase.plot accepts path_marker and path_marker_reverse but never reads them (the path is drawn from line/line_r). The book's figure scripts fig5_16.py and fig5_20.py pass path_marker=, so they are drawn in the default style (Rename RTB plot style arguments to <thing>_style in figure scripts RVC3-python#55).
• EKF.plot_map(ellipse=...) takes the covariance block P_est[i:i+2, i:i+2] for landmark i; it should be rows and columns 2i..2i+2 (plus 3 when the vehicle is estimated), so ellipses after the first are wrong.

No library code is changed.

🤖 Generated with Claude Code

[codacy-production]

Not up to standards ⛔

🔴 Issues 1 high

Alerts:
⚠ 1 issue (≤ 0 issues of at least minor severity)

Results:
1 new issue

Category	Results
ErrorProne	1 high

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🟢 Metrics 35 complexity · 1 duplication

Metric	Results
Complexity	35
Duplication	1

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (07090ed) to head (5a694fa).

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #777   +/-   ##
=====================================
  Coverage   0.00%   0.00%           
=====================================
  Files        144     144           
  Lines      14689   14689           
=====================================
  Misses     14689   14689           

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