Avoid matplotlib testing problems on Travis-CI

skimage/draw/draw.py

@@ -6,6 +6,11 @@ from ._draw import _coords_inside_image
 from .._shared._geometry import polygon_clip
 from ._draw import line
 
+from skimage._shared.version_requirements import is_installed
+matplotlib_installed = is_installed('matplotlib')
+if not matplotlib_installed:
+    warn('Polygon perimeter drawing requires matplotlib')
+
 
 def _ellipse_in_shape(shape, center, radiuses):
     """Generate coordinates of points within ellipse bounded by shape."""