bpo-28029: Make "".replace("", s, n) returning s for any n != 0. (GH-16981)

diff --git a/Lib/test/string_tests.py b/Lib/test/string_tests.py
index 38da941..948e2a3 100644
--- a/Lib/test/string_tests.py
+++ b/Lib/test/string_tests.py
@@ -505,6 +505,7 @@
         EQ("", "", "replace", "A", "")
         EQ("", "", "replace", "A", "A")
         EQ("", "", "replace", "", "", 100)
+        EQ("A", "", "replace", "", "A", 100)
         EQ("", "", "replace", "", "", sys.maxsize)
 
         # interleave (from=="", 'to' gets inserted everywhere)