Issue #15866: The xmlcharrefreplace error handler no more produces two XML
entities for a non-BMP character on narrow build.
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index b0386f0..4e7d47d 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -1118,7 +1118,7 @@
     if (!PyArg_ParseTuple(args, "u#|s", &unicode, &length, &errors))
         return NULL;
 
-    decimal_length = length * 7; /* len('€') */
+    decimal_length = length * 10; /* len('') */
     decimal = PyBytes_FromStringAndSize(NULL, decimal_length);
     if (decimal == NULL)
         return NULL;