[MAINT][WIP] Add pytest-mpl unit tests to check ouput changes in plots

nilearn/plotting/tests/test_img_plotting/test_baseline_comparisons.py

@@ -0,0 +1,70 @@
+"""
+Test if public plotting functions' output has changed.
+
+Sometimes, the output of a plotting function may unintentionanly change as a
+side effect of changing another function or piece of code that it depends on.
+These tests ensure that the outputs are not accidentally changed.
+
+Failures are expected at times when the output is changed intentionally
+(e.g. fixing a bug or adding features) for a particular function. In such
+cases, the output needs to be manually/visually checked as part of the PR
+review process and then a new baseline set for comparison.
+
+Set a new baseline by running:
+
+pytest nilearn/plotting/tests/test_img_plotting/test_baseline_comparisons.py \
+--mpl-generate-path=nilearn/plotting/tests/test_img_plotting/baseline
+
+"""
+
+import pytest
+
+from nilearn.plotting import (
+    plot_anat,
+    plot_carpet,
+    plot_epi,
+    plot_glass_brain,
+    plot_img,
+    plot_prob_atlas,
+    plot_roi,
+    plot_stat_map,
+)
+from nilearn.plotting.img_plotting import MNI152TEMPLATE
+
+PLOTTING_FUNCS_3D = {
+    plot_img,
+    plot_anat,
+    plot_stat_map,
+    plot_roi,
+    plot_epi,
+    plot_glass_brain,
+}
+
+PLOTTING_FUNCS_4D = {plot_prob_atlas, plot_carpet}
+
+
+@pytest.mark.mpl_image_compare
+@pytest.mark.parametrize("plot_func", PLOTTING_FUNCS_3D)
+def test_plot_functions_3d_default_params(plot_func, img_3d_mni):
+    """Smoke tests for 3D plotting functions with default parameters."""
+    return plot_func(img_3d_mni)
+
+
+@pytest.mark.mpl_image_compare
+def test_plot_carpet_default_params(img_4d_mni, img_3d_ones_mni):
+    """Smoke-test for 4D plot_carpet with default arguments."""
+    return plot_carpet(img_4d_mni, mask_img=img_3d_ones_mni)
+
+
+@pytest.mark.mpl_image_compare
+def test_plot_prob_atlas_default_params(img_3d_mni, img_4d_mni):
+    """Smoke-test for plot_prob_atlas with default arguments."""
+    return plot_prob_atlas(img_4d_mni, bg_img=img_3d_mni)
+
+
+@pytest.mark.mpl_image_compare
+@pytest.mark.parametrize("anat_img", [False, MNI152TEMPLATE])
+@pytest.mark.parametrize("display_mode", ["z", "ortho"])
+def test_plot_anat_MNI(anat_img, display_mode, tmp_path):
+    """Tests for plot_anat with MNI template."""
+    return plot_anat(anat_img=anat_img, display_mode=display_mode)

tox.ini

@@ -47,6 +47,7 @@ deps =
     plotly
     kaleido ; platform_system != 'Windows'
     kaleido==0.1.0.post1 ; platform_system == 'Windows'
+    pytest-mpl
 
 
 ; COMMANDS
@@ -85,8 +86,9 @@ extras = test
 deps =
     {[plotting]deps}
 commands =
-	{[testenv:test_latest]commands}
+    {[testenv:test_latest]commands}
     {[testenv:test_doc]commands}
+    {[testenv:test_pytest_mpl]commands}
 
 [testenv:test_doc]
 description = run tests on doc
@@ -142,6 +144,12 @@ deps =
 commands =
     pytest --pyargs nilearn --random-order {posargs:}
 
+[testenv:test_pytest_mpl]
+description = run pytest-mpl tests
+passenv = USERNAME
+commands =
+    pytest nilearn/plotting/tests/test_img_plotting/test_baseline_comparisons.py --mpl
+
 [testenv:test_numpy2]
 description = run tests on latest version of all dependencies
 passenv = USERNAME