Make test_imagegrid_cbar_mode_edge less flaky.

QuLogic · QuLogic · commit 95aa9683071c · 2020-03-07T00:16:35.000-05:00
Since parametrizing the test allows it to run in parallel, this makes it
flaky, as one process can overwrite the test result image of another.

Our standard way for dealing with tests that use the same baseline image
is to pass duplicate filenames to `image_comparison`, because that is
serialized.
diff --git a/lib/mpl_toolkits/tests/test_axes_grid.py b/lib/mpl_toolkits/tests/test_axes_grid.py
@@ -12,10 +12,16 @@
 # The original version of this test relied on mpl_toolkits's slightly different
 # colorbar implementation; moving to matplotlib's own colorbar implementation
 # caused the small image comparison error.
-@pytest.mark.parametrize("legacy_colorbar", [False, True])
-@image_comparison(['imagegrid_cbar_mode.png'],
+@image_comparison(['imagegrid_cbar_mode.png', 'imagegrid_cbar_mode.png'],
                   remove_text=True, style='mpl20', tol=0.3)
-def test_imagegrid_cbar_mode_edge(legacy_colorbar):
+def test_imagegrid_cbar_mode_edge():
+    # Note, we don't use @pytest.mark.parametrize, because in parallel this
+    # might cause one process result to overwrite another's.
+    for legacy_colorbar in [False, True]:
+        _test_imagegrid_cbar_mode_edge(legacy_colorbar)
+
+
+def _test_imagegrid_cbar_mode_edge(legacy_colorbar):
     mpl.rcParams["mpl_toolkits.legacy_colorbar"] = legacy_colorbar
 
     X, Y = np.meshgrid(np.linspace(0, 6, 30), np.linspace(0, 6, 30))
