Don't fail tests if cairo dependency is not installed. (matplotlib#12835)

anntzer · timhoffm · commit e0c918589ff5 · 2018-11-20T21:58:53.000+01:00
* Don't fail tests if cairo dependency is not installed.

* Only skip cairo import errors for testing
diff --git a/lib/matplotlib/testing/conftest.py b/lib/matplotlib/testing/conftest.py
@@ -43,7 +43,16 @@ def mpl_test_settings(request):
             # This import must come after setup() so it doesn't load the
             # default backend prematurely.
             import matplotlib.pyplot as plt
-            plt.switch_backend(backend)
+            try:
+                plt.switch_backend(backend)
+            except ImportError as exc:
+                # Should only occur for the cairo backend tests, if neither
+                # pycairo nor cairocffi are installed.
+                if 'cairo' in backend.lower():
+                    pytest.skip("Failed to switch to backend {} ({})."
+                                .format(backend, exc))
+                else:
+                    raise
         with warnings.catch_warnings():
             warnings.simplefilter("ignore", MatplotlibDeprecationWarning)
             matplotlib.style.use(style)
