diff --git a/doorstop/core/tests/test_item.py b/doorstop/core/tests/test_item.py
index 2ca35c7d..07431541 100644
--- a/doorstop/core/tests/test_item.py
+++ b/doorstop/core/tests/test_item.py
@@ -7,9 +7,9 @@
 import unittest
 from unittest.mock import MagicMock, Mock, patch
 
+import doorstop.core.editor
 from doorstop import common, settings
 from doorstop.common import DoorstopError
-import doorstop.core.editor
 from doorstop.core.item import Item, UnknownItem
 from doorstop.core.tests import (
     EMPTY,
@@ -476,7 +476,7 @@ def test_edit(self, mock_launch, mock_load):
     @patch("doorstop.core.editor.sys.platform", "nt")
     @patch("doorstop.core.editor.shutil.which")
     @patch("doorstop.core.editor._call")
-    def test_launch_os_nt_cygwin(self,  mock_call, mock_which):
+    def test_launch_os_nt_cygwin(self, mock_call, mock_which):
         mock_call.side_effect = FileNotFoundError
         mock_which.return_value = "cygstart"
         self.assertRaises(DoorstopError, doorstop.core.editor.launch, "")
@@ -507,6 +507,16 @@ def test_launch_os_posix(self, mock_call):
         self.assertRaises(DoorstopError, doorstop.core.editor.launch, "")
         mock_call.assert_called_once_with(["xdg-open", ""])
 
+    @patch("doorstop.core.editor.os.name", "unknown")
+    @patch("doorstop.core.editor.sys.platform", "unknown")
+    @patch("doorstop.core.editor.shutil.which")
+    @patch("doorstop.core.editor._call")
+    def test_launch_os_unknown(self, mock_call, mock_which):
+        mock_call.side_effect = FileNotFoundError
+        mock_which.return_value = "unknown"
+        self.assertRaises(DoorstopError, doorstop.core.editor.launch, "")
+        mock_call.assert_not_called()
+
     def test_link(self):
         """Verify links can be added to an item."""
         self.item.link("abc")