TST: test for add_lines working as expected

Author: jklymak

lib/matplotlib/tests/baseline_images/test_contour/contour_addlines.png

@@ -401,3 +401,16 @@ def test_contourf_log_extension():
     plt.colorbar(c1, ax=ax1)
     plt.colorbar(c2, ax=ax2)
     plt.colorbar(c3, ax=ax3)
+
+
+@image_comparison(baseline_images=['contour_addlines'],
+                  extensions=['png'], remove_text=True, style='mpl20')
+def test_contour_addlines():
+    fig, ax = plt.subplots()
+    np.random.seed(19680812)
+    X = np.random.rand(10, 10)*10000
+    pcm = ax.pcolormesh(X)
+    # add 1000 to make colors visible...
+    cont = ax.contour(X+1000)
+    cb = fig.colorbar(pcm)
+    cb.add_lines(cont)