Avoid race conditions when running tests with xdist

tests/conftest.py

@@ -1,3 +1,4 @@
+import os
 import shutil
 
 import pytest
@@ -5,12 +6,15 @@ from utils import FIXTURES_DIR, TOX4
 
 
 @pytest.fixture(autouse=True)
-def projdir(tmp_path, monkeypatch):
+def projdir(tmp_path, monkeypatch, worker_id):
     pwd = tmp_path / "projdir"
     pwd.mkdir()
     for fname in "tox.ini", "setup.py":
         shutil.copy(FIXTURES_DIR / fname, pwd)
     monkeypatch.chdir(pwd)
+    # https://github.com/pypa/pip/issues/5345#issuecomment-386424455
+    monkeypatch.setenv("XDG_CACHE_HOME",
+                       os.path.expanduser(f"~/.cache/pytest-xdist-{worker_id}"))
     return pwd
 
 

tests/fixtures/tox.ini

@@ -2,6 +2,8 @@
 envlist = py36,py37,py38,py39,py310,py311
 
 [testenv]
+passenv =
+    XDG_CACHE_HOME
 deps =
     six
     py