Ensure relpath is executed on paths in the same drive (#7335)

On Windows you can have several drives (`C:`, `D:`, ...), that is the roughly (really roughly) equivalent of mount points, since each drive is usually associated to a specific physical partition.

So you can have paths like `C:\one\path`, `D:\another\path`.

In parallel, `os.path.relpath(path, start='.')` calculates the relative path between the given `path` and a `start` path (current directory if not provided). In recent versions of Python, `os.path.relpath` will fail if `path` and `start` are not on the same drive, because a relative path between two paths like `C:\one\path`, `D:\another\path` is not possible.

In saw unit tests failing because of this in two locations. This occurs when the certbot codebase that is tested is on a given drive (like `D:`) while the default temporary directory used by `tempfile` is on another drive (most of the time located in `C:` drive).

This PR fixes that.

certbot-nginx/certbot_nginx/tests/parser_test.py

@@ -30,8 +30,16 @@ class NginxParserTest(util.NginxTest): #pylint: disable=too-many-public-methods
         self.assertEqual(nparser.root, self.config_path)
 
     def test_root_absolute(self):
-        nparser = parser.NginxParser(os.path.relpath(self.config_path))
-        self.assertEqual(nparser.root, self.config_path)
+        curr_dir = os.getcwd()
+        try:
+            # On Windows current directory may be on a different drive than self.tempdir.
+            # However a relative path between two different drives is invalid. So we move to
+            # self.tempdir to ensure that we stay on the same drive.
+            os.chdir(self.temp_dir)
+            nparser = parser.NginxParser(os.path.relpath(self.config_path))
+            self.assertEqual(nparser.root, self.config_path)
+        finally:
+            os.chdir(curr_dir)
 
     def test_root_no_trailing_slash(self):
         nparser = parser.NginxParser(self.config_path + os.path.sep)

certbot/tests/cli_test.py

@@ -23,21 +23,27 @@ PLUGINS = disco.PluginsRegistry.find_all()
 
 
 class TestReadFile(TempDirTestCase):
-    '''Test cli.read_file'''
-
-
+    """Test cli.read_file"""
     def test_read_file(self):
-        rel_test_path = os.path.relpath(os.path.join(self.tempdir, 'foo'))
-        self.assertRaises(
-            argparse.ArgumentTypeError, cli.read_file, rel_test_path)
+        curr_dir = os.getcwd()
+        try:
+            # On Windows current directory may be on a different drive than self.tempdir.
+            # However a relative path between two different drives is invalid. So we move to
+            # self.tempdir to ensure that we stay on the same drive.
+            os.chdir(self.tempdir)
+            rel_test_path = os.path.relpath(os.path.join(self.tempdir, 'foo'))
+            self.assertRaises(
+                argparse.ArgumentTypeError, cli.read_file, rel_test_path)
 
-        test_contents = b'bar\n'
-        with open(rel_test_path, 'wb') as f:
-            f.write(test_contents)
+            test_contents = b'bar\n'
+            with open(rel_test_path, 'wb') as f:
+                f.write(test_contents)
 
-        path, contents = cli.read_file(rel_test_path)
-        self.assertEqual(path, os.path.abspath(path))
-        self.assertEqual(contents, test_contents)
+            path, contents = cli.read_file(rel_test_path)
+            self.assertEqual(path, os.path.abspath(path))
+            self.assertEqual(contents, test_contents)
+        finally:
+            os.chdir(curr_dir)
 
 
 class FlagDefaultTest(unittest.TestCase):