adding test case for matplotlib#2744

Author: perimosocordiae

lib/matplotlib/tests/test_lines.py

@@ -78,3 +78,11 @@ def test_set_line_coll_dash_image():
 
     np.random.seed(0)
     cs = ax.contour(np.random.randn(20, 30), linestyles=[(0, (3, 3))])
+
+
+def test_nan_is_sorted():
+    # Exercises issue from PR #2744 (NaN throwing warning in _is_sorted)
+    line = mpl.lines.Line2D([],[])
+    assert_true(line._is_sorted(np.array([1,2,3])))
+    assert_true(not line._is_sorted(np.array([1,np.nan,3])))
+