TST: fix sub process usage on windows

tacaswell · tacaswell · commit 557e56f85b60 · 2019-10-30T23:16:19.000-04:00
thanks to @story645 for sorting this out
diff --git a/lib/matplotlib/tests/test_backend_webagg.py b/lib/matplotlib/tests/test_backend_webagg.py
@@ -1,4 +1,5 @@
 import subprocess
+import os
 import sys
 import pytest
 
@@ -7,16 +8,21 @@
 def test_webagg_fallback(backend):
     if backend == "nbagg":
         pytest.importorskip("IPython")
+    env = {}
+    if os.name == "nt":
+        env = dict(os.environ)
+    else:
+        env = {"DISPLAY": ""}
+
+    env["MPLBACKEND"] = backend
+
     test_code = (
         "import os;"
-        + f"os.environ['MPLBACKEND'] = '{backend}';"
+        + f"assert os.environ['MPLBACKEND'] == '{backend}';"
         + "import matplotlib.pyplot as plt; "
         + "print(plt.get_backend());"
         f"assert '{backend}' == plt.get_backend().lower();"
     )
-    ret = subprocess.call(
-        [sys.executable, "-c", test_code],
-        env={"MPLBACKEND": backend, "DISPLAY": ""}
-    )
+    ret = subprocess.call([sys.executable, "-c", test_code], env=env)
 
     assert ret == 0
