Index: src/alter.c
==================================================================
--- src/alter.c
+++ src/alter.c
@@ -1269,11 +1269,13 @@
 }
 
 /*
 ** SQL function:
 **
-**     sqlite_rename_column(zSql, iCol, bQuote, zNew, zTable, zOld)
+**     sqlite_rename_column(...)
+**
+** The function requires exactly 10 arguments:
 **
 **   0. zSql:     SQL statement to rewrite
 **   1. type:     Type of object ("table", "view" etc.)
 **   2. object:   Name of object
 **   3. Database: Database name (e.g. "main")
@@ -1290,11 +1292,13 @@
 ** The iCol-th column (left-most is 0) of table zTable is renamed from zCol
 ** into zNew.  The name should be quoted if bQuote is true.
 **
 ** This function is used internally by the ALTER TABLE RENAME COLUMN command.
 ** It is only accessible to SQL created using sqlite3NestedParse().  It is
-** not reachable from ordinary SQL passed into sqlite3_prepare().
+** not reachable from ordinary SQL passed into sqlite3_prepare().  Except,
+** this function is reachable for testing purposes if the
+** SQLITE_TESTCTRL_INTERNAL_FUNCTIONS test-control is engaged.
 */
 static void renameColumnFunc(
   sqlite3_context *context,
   int NotUsed,
   sqlite3_value **argv

Index: src/resolve.c
==================================================================
--- src/resolve.c
+++ src/resolve.c
@@ -816,11 +816,13 @@
         if( (pDef->funcFlags & SQLITE_FUNC_INTERNAL)!=0
          && pParse->nested==0
          && sqlite3Config.bInternalFunctions==0
         ){
           /* Internal-use-only functions are disallowed unless the
-          ** SQL is being compiled using sqlite3NestedParse() */
+          ** SQL is being compiled using sqlite3NestedParse().  The
+          ** SQLITE_TESTCTRL_INTERNAL_FUNCTIONS test-control will override
+          ** this restriction for testing purposes. */
           no_such_func = 1;
           pDef = 0;
         }
       }