TST: fail gracefully if backend can not be imported

tacaswell · tacaswell · commit 774f5581bcc9 · 2019-06-10T00:10:42.000-04:00
- due to missing tk libraries
 - due to qt already being imported
diff --git a/lib/matplotlib/testing/conftest.py b/lib/matplotlib/testing/conftest.py
@@ -26,6 +26,8 @@ def mpl_test_settings(request):
             assert len(backend_marker.args) == 1, \
                 "Marker 'backend' must specify 1 backend."
             backend, = backend_marker.args
+            skip_on_importerror = backend_marker.kwargs.get(
+                'skip_on_importerror', False)
             prev_backend = matplotlib.get_backend()
 
         style = '_classic_test'  # Default of cleanup and image_comparison too.
@@ -45,7 +47,7 @@ def mpl_test_settings(request):
             except ImportError as exc:
                 # Should only occur for the cairo backend tests, if neither
                 # pycairo nor cairocffi are installed.
-                if 'cairo' in backend.lower():
+                if 'cairo' in backend.lower() or skip_on_importerror:
                     pytest.skip("Failed to switch to backend {} ({})."
                                 .format(backend, exc))
                 else:
diff --git a/lib/matplotlib/tests/test_backend_tk.py b/lib/matplotlib/tests/test_backend_tk.py
@@ -4,7 +4,7 @@
 from matplotlib.backends import _tkagg
 
 
-@pytest.mark.backend('TkAgg')
+@pytest.mark.backend('TkAgg', skip_on_importerror=True)
 def test_blit():
     def evil_blit(photoimage, aggimage, offsets, bboxptr):
         data = np.asarray(aggimage)
