Don't look up "HOME" environment variable unconditionally to avoid KeyError

if it's not defined, like on Windows which usually doesn't have "HOME", but
"HOMEDRIVE" and "HOMEPATH" instead.

dulwich/tests/__init__.py

@@ -30,10 +30,22 @@ import tempfile
 if sys.version_info >= (2, 7):
     # If Python itself provides an exception, use that
     import unittest
-    from unittest import SkipTest, TestCase
+    from unittest import SkipTest, TestCase as _TestCase
 else:
     import unittest2 as unittest
-    from unittest2 import SkipTest, TestCase
+    from unittest2 import SkipTest, TestCase as _TestCase
+
+
+class TestCase(_TestCase):
+    def makeSafeEnv(self):
+        """Modifies HOME to point to a non-existing directory to avoid
+        side-effects caused by user's ~/.gitconfig"""
+
+        if "HOME" in os.environ:
+            self.addCleanup(os.environ.__setitem__, "HOME", os.environ["HOME"])
+        else:
+            self.addCleanup(os.environ.__delitem__, "HOME")
+        os.environ["HOME"] = "/nonexistant"
 
 
 class BlackboxTestCase(TestCase):

dulwich/tests/test_config.py

@@ -171,8 +171,7 @@ class ConfigDictTests(TestCase):
 class StackedConfigTests(TestCase):
 
     def test_default_backends(self):
-        self.addCleanup(os.environ.__setitem__, "HOME", os.environ["HOME"])
-        os.environ["HOME"] = "/nonexistant"
+        self.makeSafeEnv()
         StackedConfig.default_backends()
 
 

dulwich/tests/test_repository.py

@@ -320,8 +320,7 @@ class RepositoryTests(TestCase):
         self.assertIsInstance(r.get_config(), Config)
 
     def test_get_config_stack(self):
-        self.addCleanup(os.environ.__setitem__, "HOME", os.environ["HOME"])
-        os.environ["HOME"] = "/nonexistant"
+        self.makeSafeEnv()
         r = self._repo = open_repo('ooo_merge.git')
         self.assertIsInstance(r.get_config_stack(), Config)
 
@@ -460,8 +459,7 @@ class BuildRepoTests(TestCase):
         self.assertEquals("iso8859-1", r[commit_sha].encoding)
 
     def test_commit_config_identity(self):
-        self.addCleanup(os.environ.__setitem__, "HOME", os.environ["HOME"])
-        os.environ["HOME"] = "/nonexistant"
+        self.makeSafeEnv()
         # commit falls back to the users' identity if it wasn't specified
         r = self._repo
         c = r.get_config()