TST : add test for no snapping of 'o' path

Author: tacaswell

lib/matplotlib/tests/baseline_images/test_axes/o_marker_path_snap.png

@@ -3586,6 +3586,18 @@ def test_set_get_ticklabels():
     ax[1].set_yticklabels(ax[0].get_yticklabels() )
 
 
+@image_comparison(baseline_images=['o_marker_path_snap'], extensions=['png'],
+                  savefig_kwarg={'dpi': 72})
+def test_o_marker_path_snap():
+    fig, ax = plt.subplots()
+    ax.margins(.1)
+    for ms in range(1, 15):
+        ax.plot([1, 2, ], np.ones(2) + ms, 'o', ms=ms)
+
+    for ms in np.linspace(1, 10, 25):
+        ax.plot([3, 4, ], np.ones(2) + ms, 'o', ms=ms)
+
+
 @cleanup
 def test_margins():
     # test all ways margins can be called