Ensure backend is set for subprocess'd tests.

This keeps them working even if the user has a backend set in their
config that is not available in the test environment.

Author: QuLogic

lib/matplotlib/tests/test_determinism.py

@@ -100,7 +100,8 @@ def test_determinism_check(objects, fmt, usetex):
             [sys.executable, "-R", "-c",
              f"from matplotlib.tests.test_determinism import _save_figure;"
              f"_save_figure({objects!r}, {fmt!r}, {usetex})"],
-            env={**os.environ, "SOURCE_DATE_EPOCH": "946684800"})
+            env={**os.environ, "SOURCE_DATE_EPOCH": "946684800",
+                 "MPLBACKEND": "Agg"})
         for _ in range(3)
     ]
     for p in plots[1:]:
@@ -139,5 +140,6 @@ def test_determinism_source_date_epoch(fmt, string):
         [sys.executable, "-R", "-c",
          f"from matplotlib.tests.test_determinism import _save_figure; "
          f"_save_figure('', {fmt!r})"],
-        env={**os.environ, "SOURCE_DATE_EPOCH": "946684800"})
+        env={**os.environ, "SOURCE_DATE_EPOCH": "946684800",
+             "MPLBACKEND": "Agg"})
     assert string in buf

lib/matplotlib/tests/test_matplotlib.py

@@ -56,4 +56,4 @@ def test_importable_with__OO():
         "import matplotlib.patches as mpatches"
     )
     cmd = [sys.executable, "-OO", "-c", program]
-    assert subprocess.call(cmd) == 0
+    assert subprocess.call(cmd, env={**os.environ, "MPLBACKEND": ""}) == 0

lib/matplotlib/tests/test_sphinxext.py

@@ -1,6 +1,7 @@
 """Tests for tinypages build using sphinx extensions."""
 
 import filecmp
+import os
 from pathlib import Path
 from subprocess import Popen, PIPE
 import sys
@@ -19,14 +20,14 @@ def test_tinypages(tmpdir):
     cmd = [sys.executable, '-msphinx', '-W', '-b', 'html',
            '-d', str(doctree_dir),
            str(Path(__file__).parent / 'tinypages'), str(html_dir)]
-    proc = Popen(cmd, stdout=PIPE, stderr=PIPE, universal_newlines=True)
+    proc = Popen(cmd, stdout=PIPE, stderr=PIPE, universal_newlines=True,
+                 env={**os.environ, "MPLBACKEND": ""})
     out, err = proc.communicate()
 
     assert proc.returncode == 0, \
-        "sphinx build failed with stdout:\n{}\nstderr:\n{}\n".format(out, err)
+        f"sphinx build failed with stdout:\n{out}\nstderr:\n{err}\n"
     if err:
-        pytest.fail("sphinx build emitted the following warnings:\n{}"
-                    .format(err))
+        pytest.fail(f"sphinx build emitted the following warnings:\n{err}")
 
     assert html_dir.is_dir()