The usual.
diff --git a/Lib/dos-8x3/test_sup.py b/Lib/dos-8x3/test_sup.py
index 7dc1940..3839c79 100755
--- a/Lib/dos-8x3/test_sup.py
+++ b/Lib/dos-8x3/test_sup.py
@@ -41,3 +41,15 @@
 
 TESTFN = '@test' # Filename used for testing
 from os import unlink
+
+def findfile(file, here=__file__):
+	import os
+	if os.path.isabs(file):
+		return file
+	import sys
+	path = sys.path
+	path = [os.path.dirname(here)] + path
+	for dn in path:
+		fn = os.path.join(dn, file)
+		if os.path.exists(fn): return fn
+	return file