Might as well go for 100% coverage.

src/napari_matplotlib/tests/scatter/test_scatter.py

@@ -2,7 +2,7 @@
 
 import pytest
 
-from napari_matplotlib import ScatterWidget
+from napari_matplotlib import ScatterBaseWidget, ScatterWidget
 
 
 @pytest.mark.mpl_image_compare
@@ -48,3 +48,10 @@ def test_scatter_3D(make_napari_viewer, brain_data):
     viewer.layers.selection.add(viewer.layers[1])
 
     return deepcopy(fig)
+
+
+def test_get_data_notimplemented_on_base(make_napari_viewer):
+    viewer = make_napari_viewer()
+    widget = ScatterBaseWidget(viewer)
+    with pytest.raises(NotImplementedError):
+        widget._get_data()

src/napari_matplotlib/tests/test_util.py

@@ -28,6 +28,9 @@ def test_interval():
     with pytest.raises(ValueError, match="must be an integer"):
         "string" in interval  # type: ignore
 
+    with pytest.raises(ValueError, match="must be <= upper_bound"):
+        Interval(5, 3)
+
 
 @pytest.mark.parametrize(
     "lower, upper, text",