Use Agg backend, draw each plot

properties/test_plotting.py

@@ -6,9 +6,14 @@
     2. Plotting is stateful, so we have to clean up after each call
 With those details taken care of, they all pass!
 
+Note also that a pytest teardown fixture (or unittest method) would not work
+here, as they run once per test and we need to clean up once per *example*.
+
 """
 from __future__ import absolute_import, division, print_function
 
+import matplotlib
+matplotlib.use('Agg')
 import matplotlib.pyplot as plt
 
 from hypothesis import given, settings
@@ -39,22 +44,26 @@ def test_imshow(arr):
     # Note that we clear the plot after each call - otherwise we just get
     # errors from polluting state with too many colormaps!
     xr.DataArray(arr).plot.imshow()
+    plt.draw()
     plt.clf()
 
 
 @given(two_dimensional_array)
 def test_pcolormesh(arr):
     xr.DataArray(arr).plot.pcolormesh()
+    plt.draw()
     plt.clf()
 
 
 @given(two_dimensional_array)
 def test_contour(arr):
     xr.DataArray(arr).plot.contour()
+    plt.draw()
     plt.clf()
 
 
 @given(two_dimensional_array)
 def test_contourf(arr):
     xr.DataArray(arr).plot.contourf()
+    plt.draw()
     plt.clf()