Make tmpdir more resilient in case environment variables required by getpass are missing

Fix #1010

_pytest/tmpdir.py

@@ -56,7 +56,11 @@ class TempdirFactory:
                 # make_numbered_dir() call
                 import getpass
                 temproot = py.path.local.get_temproot()
+                try:
                     rootdir = temproot.join('pytest-of-%s' % getpass.getuser())
+                except ImportError:
+                    # see issue #1010
+                    rootdir = temproot.join('pytest-tox')
                 rootdir.ensure(dir=1)
                 basetemp = py.path.local.make_numbered_dir(prefix='pytest-',
                                                            rootdir=rootdir)

testing/test_tmpdir.py

@@ -118,3 +118,18 @@ def test_tmpdir_factory(testdir):
     """)
     reprec = testdir.inline_run()
     reprec.assertoutcome(passed=1)
+
+
+def test_tmpdir_fallback_tox_env(testdir, monkeypatch):
+    """Test that tmpdir works even if environment variables required by getpass
+    module are missing (#1010).
+    """
+    monkeypatch.delenv('USER', raising=False)
+    monkeypatch.delenv('USERNAME', raising=False)
+    testdir.makepyfile("""
+        import pytest
+        def test_some(tmpdir):
+            assert tmpdir.isdir()
+    """)
+    reprec = testdir.inline_run()
+    reprec.assertoutcome(passed=1)