Add tests for color_continuous_scale autocolorscale behavior

Add tests to verify that user-provided color_continuous_scale overrides
template autocolorscale=True, and that template autocolorscale is respected
when user doesn't provide a colorscale.

Changes:
- tests/test_optional/test_px/test_colors.py: Add test_color_continuous_scale_autocolorscale()
- tests/test_optional/test_px/test_imshow.py: Add test_imshow_color_continuous_scale_autocolorscale()

Author: antonymilne

plotly/express/_core.py

@@ -2489,8 +2489,7 @@ def make_figure(args, constructor, trace_patch=None, layout_patch=None):
     # Track if color_continuous_scale was explicitly provided by user
     # (before apply_default_cascade fills it from template/defaults)
     user_provided_colorscale = (
-        "color_continuous_scale" in args
-        and args["color_continuous_scale"] is not None
+        "color_continuous_scale" in args and args["color_continuous_scale"] is not None
     )
     apply_default_cascade(args)
 

plotly/express/_imshow.py

@@ -236,8 +236,7 @@ def imshow(
     # Track if color_continuous_scale was explicitly provided by user
     # (before apply_default_cascade fills it from template/defaults)
     user_provided_colorscale = (
-        "color_continuous_scale" in args
-        and args["color_continuous_scale"] is not None
+        "color_continuous_scale" in args and args["color_continuous_scale"] is not None
     )
     apply_default_cascade(args)
     labels = labels.copy()

tests/test_optional/test_px/test_colors.py

@@ -60,3 +60,24 @@ def test_color_categorical_dtype():
     px.scatter(
         df[df.day != df.day.cat.categories[0]], x="total_bill", y="tip", color="day"
     )
+
+
+def test_color_continuous_scale_autocolorscale():
+    # User-provided colorscale should override template autocolorscale=True
+    fig = px.scatter(
+        x=[1, 2],
+        y=[1, 2],
+        color=[1, 2],
+        color_continuous_scale="Viridis",
+        template=dict(layout_coloraxis_autocolorscale=True),
+    )
+    assert fig.layout.coloraxis1.autocolorscale is False
+
+    # Without user-provided colorscale, template autocolorscale should be respected
+    fig2 = px.scatter(
+        x=[1, 2],
+        y=[1, 2],
+        color=[1, 2],
+        template=dict(layout_coloraxis_autocolorscale=True),
+    )
+    assert fig2.layout.coloraxis1.autocolorscale is None

tests/test_optional/test_px/test_imshow.py

@@ -98,6 +98,23 @@ def test_colorscale():
     assert fig.layout.coloraxis1.colorscale[0] == (0.0, "#440154")
 
 
+def test_imshow_color_continuous_scale_autocolorscale():
+    # User-provided colorscale should override template autocolorscale=True
+    fig = px.imshow(
+        img_gray,
+        color_continuous_scale="Viridis",
+        template=dict(layout_coloraxis_autocolorscale=True),
+    )
+    assert fig.layout.coloraxis1.autocolorscale is False
+
+    # Without user-provided colorscale, template autocolorscale should be respected
+    fig2 = px.imshow(
+        img_gray,
+        template=dict(layout_coloraxis_autocolorscale=True),
+    )
+    assert fig2.layout.coloraxis1.autocolorscale is None
+
+
 def test_wrong_dimensions():
     imgs = [1, np.ones((5,) * 3), np.ones((5,) * 4)]
     msg = "px.imshow only accepts 2D single-channel, RGB or RGBA images."