Test for drawing mask contour on a transparent background.

test/test_wordcloud.py

@@ -229,6 +229,17 @@ def test_mask_contour():
     assert_true(all(sm_array[100, 300] == [0, 0, 255]))
 
 
+def test_mask_contour_transparent():
+    # test if mask contour can be drawn on a transparent background
+    # https://github.com/amueller/word_cloud/pull/389
+    mask = np.ones((600, 600, 3), dtype='ubyte')
+    mask[:, -10:] = 0
+    w = WordCloud(mode='RGBA', background_color=None, contour_color='blue', contour_width=2, mask=mask,
+                  max_words=50, width=800, height=800)
+    w.generate(THIS)
+    img = w.to_image()
+
+
 def test_single_color_func():
     # test single color function for different color formats
     random = Random(42)