diff --git a/ext/jni/src/c/sqlite3-jni.c b/ext/jni/src/c/sqlite3-jni.c
index a46429bc58..9cb02cfb4c 100644
--- a/ext/jni/src/c/sqlite3-jni.c
+++ b/ext/jni/src/c/sqlite3-jni.c
@@ -4016,9 +4016,90 @@ JDECLFtsXA(jobject,xUserData)(JENV_OSELF,jobject jFcx){
 #endif /* SQLITE_ENABLE_FTS5 */
 
 ////////////////////////////////////////////////////////////////////////
-// End of the main API bindings. What follows are internal utilities.
+// End of the main API bindings. Start of SQLTester bits...
 ////////////////////////////////////////////////////////////////////////
 
+typedef struct SQLTesterJni SQLTesterJni;
+struct SQLTesterJni {
+  sqlite3_int64 nDup;
+};
+static SQLTesterJni SQLTester = {
+  0
+};
+
+static void SQLTester_dup_destructor(void*pToFree){
+  u64 *p = (u64*)pToFree;
+  assert( p!=0 );
+  p--;
+  assert( p[0]==0x2bbf4b7c );
+  p[0] = 0;
+  p[1] = 0;
+  sqlite3_free(p);
+}
+
+/*
+** Implementation of
+**
+**         dup(TEXT)
+**
+** This SQL function simply makes a copy of its text argument.  But it
+** returns the result using a custom destructor, in order to provide
+** tests for the use of Mem.xDel() in the SQLite VDBE.
+*/
+static void SQLTester_dup_func(
+  sqlite3_context *context,
+  int argc,
+  sqlite3_value **argv
+){
+  u64 *pOut;
+  char *z;
+  int n = sqlite3_value_bytes(argv[0]);
+  SQLTesterJni * const p = (SQLTesterJni *)sqlite3_user_data(context);
+
+  ++p->nDup;
+  if( n>0 && (pOut = sqlite3_malloc( (n+16)&~7 ))!=0 ){
+    pOut[0] = 0x2bbf4b7c;
+    z = (char*)&pOut[1];
+    memcpy(z, sqlite3_value_text(argv[0]), n);
+    z[n] = 0;
+    sqlite3_result_text(context, z, n, SQLTester_dup_destructor);
+  }
+  return;
+}
+
+/*
+** Return the number of calls to the dup() SQL function since the
+** SQLTester context was opened or since the last dup_count() call.
+*/
+static void SQLTester_dup_count_func(
+  sqlite3_context *context,
+  int argc,
+  sqlite3_value **argv
+){
+  SQLTesterJni * const p = (SQLTesterJni *)sqlite3_user_data(context);
+  sqlite3_result_int64(context, p->nDup);
+  p->nDup = 0;
+}
+
+static int SQLTester_auto_extension(sqlite3 *pDb, const char **pzErr,
+                                    const struct sqlite3_api_routines *ignored){
+  sqlite3_create_function(pDb, "dup", 1, SQLITE_UTF8, &SQLTester,
+                          SQLTester_dup_func, 0, 0);
+  sqlite3_create_function(pDb, "dup_count", 0, SQLITE_UTF8, &SQLTester,
+                          SQLTester_dup_count_func, 0, 0);
+  return 0;
+}
+
+JNIEXPORT void JNICALL
+Java_org_sqlite_jni_tester_SQLTester_installCustomExtensions(JENV_CSELF){
+  sqlite3_auto_extension( (void(*)(void))SQLTester_auto_extension );
+}
+
+////////////////////////////////////////////////////////////////////////
+// End of SQLTester bindings. Start of lower-level bits.
+////////////////////////////////////////////////////////////////////////
+
+
 /**
    Uncaches the current JNIEnv from the S3JniGlobal state, clearing any
    resources owned by that cache entry and making that slot available
@@ -4030,18 +4111,6 @@ Java_org_sqlite_jni_SQLite3Jni_uncacheJniEnv(JENV_CSELF){
   return S3JniGlobal_env_uncache(env) ? JNI_TRUE : JNI_FALSE;
 }
 
-static int SQLTester_auto_extension(sqlite3 *pDb, const char **pzErr,
-                                    const struct sqlite3_api_routines *ignored){
-  //MARKER(("TODO: DUP() UDF\n"));
-  return 0;
-}
-
-
-JNIEXPORT void JNICALL
-Java_org_sqlite_jni_tester_SQLTester_installCustomExtensions(JENV_CSELF){
-  sqlite3_auto_extension( (void(*)(void))SQLTester_auto_extension );
-}
-
 /**
    Called during static init of the SQLite3Jni class to sync certain
    compile-time constants to Java-space.
diff --git a/ext/jni/src/org/sqlite/jni/tester/SQLTester.java b/ext/jni/src/org/sqlite/jni/tester/SQLTester.java
index 1629bde603..c1995f8577 100644
--- a/ext/jni/src/org/sqlite/jni/tester/SQLTester.java
+++ b/ext/jni/src/org/sqlite/jni/tester/SQLTester.java
@@ -156,9 +156,9 @@ public class SQLTester {
 
   int getCurrentDbId(){ return iCurrentDb; }
 
-  SQLTester affirmDbId(int n) throws Exception{
+  SQLTester affirmDbId(int n) throws IndexOutOfBoundsException {
     if(n<0 || n>=aDb.length){
-      Util.toss(IllegalArgumentException.class,"illegal db number.");
+      throw new IndexOutOfBoundsException("illegal db number.");
     }
     return this;
   }
@@ -169,6 +169,10 @@ public class SQLTester {
 
   sqlite3 getCurrentDb(){ return aDb[iCurrentDb]; }
 
+  sqlite3 getDbById(int id) throws Exception{
+    return affirmDbId(id).aDb[iCurrentDb];
+  }
+
   void closeDb(int id) throws Exception{
     final sqlite3 db = affirmDbId(id).aDb[id];
     if( null != db ){
@@ -533,11 +537,12 @@ class ResultCommand extends Command {
 
 class RunCommand extends Command {
   public RunCommand(SQLTester t, String[] argv, String content) throws Exception{
-    argcCheck(argv,0);
+    argcCheck(argv,0,1);
     affirmHasContent(content);
-    int rc = t.execSql(null, false, false, content);
+    final sqlite3 db = (1==argv.length)
+      ? t.getCurrentDb() : t.getDbById( Integer.parseInt(argv[1]) );
+    int rc = t.execSql(db, false, false, content);
     if( 0!=rc ){
-      sqlite3 db = t.getCurrentDb();
       String msg = sqlite3_errmsg(db);
       t.verbose(argv[0]," non-fatal command error #",rc,": ",
                 msg,"\nfor SQL:\n",content);
diff --git a/manifest b/manifest
index 2b3dc8f488..8d6f499abf 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Correct\s--result\sarg\scount\scheck\sand\sadd\sinfrastructure\sto\slet\sus\sadd\scustom\sC-side\sbehavior\sto\sSQLTester\svia\san\sauto\sextension.
-D 2023-08-08T20:41:29.013
+C Add\sSQLTester\sdup()\sand\sdup_count()\sUDFs.\sCorrect\sarg\shandling\sof\sthe\s--run\scommand.
+D 2023-08-08T21:05:39.810
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -232,7 +232,7 @@ F ext/icu/icu.c c074519b46baa484bb5396c7e01e051034da8884bad1a1cb7f09bbe6be3f0282
 F ext/icu/sqliteicu.h fa373836ed5a1ee7478bdf8a1650689294e41d0c89c1daab26e9ae78a32075a8
 F ext/jni/GNUmakefile dcd9595bf9b218c8c97a60f558eaacedbd3901f63ed59475f38c73a7692dd084
 F ext/jni/README.md e965674505e105626127ad45e628e4d19fcd379cdafc4d23c814c1ac2c55681d
-F ext/jni/src/c/sqlite3-jni.c 6ab1fa79b54b918e63f8ad02b97ed99300b1904ac8542b224fc819a3e7b41c60
+F ext/jni/src/c/sqlite3-jni.c 684d22ba352c300118a05918081b7219926469252c904896aa86c3a31025dbe1
 F ext/jni/src/c/sqlite3-jni.h ec38592e88d32f09ba4bde13f2e135bb7cf8712356b807df521b3fc99edeab32
 F ext/jni/src/org/sqlite/jni/Authorizer.java 1308988f7f40579ea0e4deeaec3c6be971630566bd021c31367fe3f5140db892
 F ext/jni/src/org/sqlite/jni/AutoExtension.java 3409ad8954d6466bf772e6be9379e0e337312b446b668287062845755a16844d
@@ -266,7 +266,7 @@ F ext/jni/src/org/sqlite/jni/sqlite3_context.java d26573fc7b309228cb49786e907859
 F ext/jni/src/org/sqlite/jni/sqlite3_stmt.java 78e6d1b95ac600a9475e9db4623f69449322b0c93d1bd4e1616e76ed547ed9fc
 F ext/jni/src/org/sqlite/jni/sqlite3_value.java 3d1d4903e267bc0bc81d57d21f5e85978eff389a1a6ed46726dbe75f85e6914a
 F ext/jni/src/org/sqlite/jni/tester/Outer.java 3d9c40f8ed58ec0df05ca160986ea06ec84ec1f338b069cfba9604bbba467a01
-F ext/jni/src/org/sqlite/jni/tester/SQLTester.java 1a7fe4607b80336f0bcb5e0cb7237d987d42c1dfdf59029566c3bc75c2053fbe
+F ext/jni/src/org/sqlite/jni/tester/SQLTester.java 1d54d137405287b7b88b9428134c6208f2c60fb01ad5d0e9126829e4044df1a7
 F ext/jni/src/org/sqlite/jni/tester/TestScript.java 52350fb458d7d2816377a824c18c498c4a97f0026b64278f62ff1c382a92a070
 F ext/jni/src/org/sqlite/jni/tester/test-script-interpreter.md 4a4868c70a68aa1829c1f7659daa78198187199d176778efb86a239c9e58802c
 F ext/jni/src/tests/000_first.test bd912c4d88f4f85264de1b53267114891bdb4c6d0d2e847343bc3ff482ec296e
@@ -2090,8 +2090,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 49005ca5cc191c52279bc7fdb45d95eeb6f8e344f78ce9dbd97aac814bc21202
-R 2e62d651a234281d8736039a6472287a
+P bb8321702eea52fa9d42987a4b053b32d8eba15580a39d7831cd8d6f1ceb62bf
+R 20b8372fe27975edee36fa6d84512581
 U stephan
-Z 6b00d1de9eb6d40c30f757066262f00c
+Z 9a23750fa7c3396fc72fc1349e829a3b
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 40daf0cb7f..8685b309a3 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-bb8321702eea52fa9d42987a4b053b32d8eba15580a39d7831cd8d6f1ceb62bf
\ No newline at end of file
+0dba3073f44685a51a5db7ff8886295fe04dfd43f69cbf53ad3d5afce741076b
\ No newline at end of file