Add theme test

Author: dstansby

Diff for: src/napari_matplotlib/tests/baseline/test_custom_theme.png

@@ -1,4 +1,5 @@
 import os
+from pathlib import Path
 
 import numpy as np
 import pytest
@@ -52,3 +53,8 @@ def set_strict_qt():
         os.environ[env_var] = old_val
     else:
         del os.environ[env_var]
+
+
+@pytest.fixture
+def theme_path():
+    return Path(__file__).parent / "data" / "test_theme.mplstyle"

Diff for: src/napari_matplotlib/tests/conftest.py

@@ -0,0 +1,15 @@
+# Dark-theme napari colour scheme for matplotlib plots
+
+#f4b8b2 # light red
+#b2e4f4 # light blue
+#0aa3fc # dark blue
+#008939 # dark green
+
+figure.facecolor    : f4b8b2 # light red
+axes.facecolor      : b2e4f4 # light blue
+axes.edgecolor      : 0aa3fc # dark blue
+
+xtick.color         : 008939 # dark green
+xtick.labelcolor    : 008939 # dark green
+ytick.color         : 008939 # dark green
+ytick.labelcolor    : 008939 # dark green

Diff for: src/napari_matplotlib/tests/data/test_theme.mplstyle

@@ -1,3 +1,5 @@
+from copy import deepcopy
+
 import napari
 import numpy as np
 import pytest
@@ -118,3 +120,23 @@ def test_no_theme_side_effects(make_napari_viewer):
     unrelated_figure.tight_layout()
 
     return unrelated_figure
+
+
+@pytest.mark.mpl_image_compare
+def test_custom_theme(make_napari_viewer, theme_path, brain_data):
+    viewer = make_napari_viewer()
+    viewer.theme = "dark"
+
+    widget = ScatterWidget(viewer)
+    widget.mpl_style_sheet_path = theme_path
+
+    viewer.add_image(brain_data[0], **brain_data[1], name="brain")
+    viewer.add_image(
+        brain_data[0] * -1, **brain_data[1], name="brain_reversed"
+    )
+
+    viewer.layers.selection.clear()
+    viewer.layers.selection.add(viewer.layers[0])
+    viewer.layers.selection.add(viewer.layers[1])
+
+    return deepcopy(widget.figure)