test: regression guard for HowToLens tutorial_3 NaN axis-limits crash

test_autolens/lens/plot/test_tracer_plots_nan_axis.py

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+"""
+Regression test for the HowToLens chapter-1 ``tutorial_3_more_ray_tracing``
+crash: ``ValueError: Axis limits cannot be NaN or Inf during plotting``.
+
+The tutorial builds a multi-plane tracer whose lens mass profiles are singular
+isothermal spheres centred on grid pixels. Historically the deflection angles
+evaluated at those singular centres produced NaN/Inf, so the traced
+source-plane grid contained non-finite coordinates; the tracer plotters then
+derived their axis limits from those coordinates and matplotlib raised
+``ValueError: Axis limits cannot be NaN or Inf``.
+
+The fix was made at the *producer*: the mass-profile deflection code now handles
+``r = 0`` (see autogalaxy "handle r=0 in ... deflections" and the NaN-safe
+masking changes), so the traced grids and images stay finite and the plotters
+receive finite extents.
+
+These tests lock that in by reproducing the tutorial-3 four-galaxy, two-plane
+tracer on a grid whose pixels coincide with the singular mass centres, and
+asserting (a) the traced grids and image remain finite and (b) the tracer
+subplots render without raising.
+"""
+import numpy as np
+import pytest
+
+import autolens as al
+from autolens.lens.plot.tracer_plots import (
+    subplot_tracer,
+    subplot_galaxies_images,
+)
+
+
+@pytest.fixture(name="grid_singular_centres")
+def make_grid_singular_centres():
+    # An odd ``shape_native`` with 0.5" pixels places pixels exactly on the
+    # singular mass centres at (0.0, 0.0) and (1.0, 0.0) -- the historical
+    # NaN/Inf trigger for the deflection angles.
+    return al.Grid2D.uniform(shape_native=(7, 7), pixel_scales=0.5)
+
+
+@pytest.fixture(name="tracer_tutorial_3")
+def make_tracer_tutorial_3():
+    # The "Multi Galaxy Ray Tracing" tracer from HowToLens tutorial 3: two lens
+    # galaxies at z=0.5 (a main lens with a singular isothermal + external shear
+    # and a satellite) and two source galaxies at z=1.0.
+    lens = al.Galaxy(
+        redshift=0.5,
+        bulge=al.lp.SersicSph(
+            centre=(0.0, 0.0), intensity=2.0, effective_radius=0.5, sersic_index=2.5
+        ),
+        mass=al.mp.Isothermal(
+            centre=(0.0, 0.0), ell_comps=(0.0, -0.111111), einstein_radius=1.6
+        ),
+        shear=al.mp.ExternalShear(gamma_1=0.05, gamma_2=0.0),
+    )
+    lens_satellite = al.Galaxy(
+        redshift=0.5,
+        bulge=al.lp.DevVaucouleursSph(
+            centre=(1.0, 0.0), intensity=2.0, effective_radius=0.2
+        ),
+        mass=al.mp.IsothermalSph(centre=(1.0, 0.0), einstein_radius=0.4),
+    )
+    source_0 = al.Galaxy(
+        redshift=1.0,
+        bulge=al.lp.DevVaucouleursSph(
+            centre=(0.1, 0.2), intensity=0.3, effective_radius=0.3
+        ),
+        disk=al.lp.ExponentialCore(
+            centre=(0.1, 0.2),
+            ell_comps=(0.111111, 0.0),
+            intensity=3.0,
+            effective_radius=2.0,
+        ),
+    )
+    source_1 = al.Galaxy(
+        redshift=1.0,
+        disk=al.lp.ExponentialCore(
+            centre=(-0.3, -0.5),
+            ell_comps=(0.1, 0.0),
+            intensity=8.0,
+            effective_radius=1.0,
+        ),
+    )
+    return al.Tracer(
+        galaxies=[lens, lens_satellite, source_0, source_1],
+        cosmology=al.cosmo.Planck15(),
+    )
+
+
+def test__traced_grids_and_image_are_finite_at_singular_mass_centres(
+    tracer_tutorial_3, grid_singular_centres
+):
+    # Producer-side guard: deflections at the singular mass centres must not
+    # introduce NaN/Inf, otherwise the plotters below would derive non-finite
+    # axis limits and crash (the original tutorial-3 failure).
+    traced = tracer_tutorial_3.traced_grid_2d_list_from(grid=grid_singular_centres)
+
+    for plane_grid in traced:
+        assert np.isfinite(np.asarray(plane_grid.array)).all()
+
+    image = tracer_tutorial_3.image_2d_from(grid=grid_singular_centres)
+
+    assert np.isfinite(np.asarray(image.array)).all()
+
+
+def test__subplot_tracer__singular_mass_centres__does_not_raise(
+    tracer_tutorial_3, grid_singular_centres, tmp_path, plot_patch
+):
+    subplot_tracer(
+        tracer=tracer_tutorial_3,
+        grid=grid_singular_centres,
+        output_path=tmp_path,
+        output_format="png",
+    )
+
+    assert str(tmp_path / "tracer.png") in plot_patch.paths
+
+
+def test__subplot_galaxies_images__singular_mass_centres__does_not_raise(
+    tracer_tutorial_3, grid_singular_centres, tmp_path, plot_patch
+):
+    subplot_galaxies_images(
+        tracer=tracer_tutorial_3,
+        grid=grid_singular_centres,
+        output_path=tmp_path,
+        output_format="png",
+    )
+
+    assert str(tmp_path / "galaxies_images.png") in plot_patch.paths