diff --git a/tests/test_dom_spot.py b/tests/test_dom_spot.py
index 620c9718d..c70da0b47 100644
--- a/tests/test_dom_spot.py
+++ b/tests/test_dom_spot.py
@@ -1,4 +1,7 @@
+import pytest
+
 from textual.widget import Widget
+from textual.dom import DOMError
 
 class Content(Widget):
     pass
@@ -7,6 +10,8 @@ class Body(Widget):
     pass
 
 def test_find_dom_spot():
+
+    # Build up a "fake" DOM for an application.
     screen = Widget(name="Screen")
     header = Widget(name="Header", id="header")
     body   = Body(id="body")
@@ -14,9 +19,21 @@ def test_find_dom_spot():
     body._add_children(*content)
     footer = Widget(name="Footer", id="footer")
     screen._add_children(header, body, footer)
+
+    # Just as a quick double-check, make sure the main components are in
+    # their intended place.
     assert list(screen.children) == [header,body,footer]
+
+    # Now check that we find what we're looking for in the places we expect
+    # to find them.
     assert screen._find_spot(None) == (screen,-1)
     assert screen._find_spot(1) == (screen, 1)
     assert screen._find_spot(body) == screen._find_spot(1)
     assert screen._find_spot("Body") == screen._find_spot(body)
     assert screen._find_spot("#body") == screen._find_spot(1)
+
+    # Finally, let's be sure that we get an error if, for some odd reason,
+    # we go looking for a widget that isn't actually part of the DOM we're
+    # looking in.
+    with pytest.raises(DOMError):
+        _ = screen._find_spot(Widget())