Fix env override in WebAgg backend test.

QuLogic · QuLogic · commit f0dbd8d7b76a · 2019-11-20T15:58:04.000-05:00
It's only necessary to override DISPLAY, not throw away the rest of the
environment. Without the other environment variables, stuff like custom
PYTHONPATH break in this test.
diff --git a/lib/matplotlib/tests/test_backend_webagg.py b/lib/matplotlib/tests/test_backend_webagg.py
@@ -8,11 +8,9 @@
 def test_webagg_fallback(backend):
     if backend == "nbagg":
         pytest.importorskip("IPython")
-    env = {}
-    if os.name == "nt":
-        env = dict(os.environ)
-    else:
-        env = {"DISPLAY": ""}
+    env = dict(os.environ)
+    if os.name != "nt":
+        env["DISPLAY"] = ""
 
     env["MPLBACKEND"] = backend
 
