diff --git a/spark/src/test/resources/sql-tests/expressions/string/string_lpad.sql b/spark/src/test/resources/sql-tests/expressions/string/string_lpad.sql
index 27b38bbda5..145aa2a42b 100644
--- a/spark/src/test/resources/sql-tests/expressions/string/string_lpad.sql
+++ b/spark/src/test/resources/sql-tests/expressions/string/string_lpad.sql
@@ -15,39 +15,47 @@
 -- specific language governing permissions and limitations
 -- under the License.
 
+-- Config: spark.comet.exec.scalaUDF.codegen.enabled=true
+
 statement
 CREATE TABLE test_lpad(s string, len int, pad string) USING parquet
 
 statement
-INSERT INTO test_lpad VALUES ('hi', 5, 'x'), ('hello', 3, 'x'), ('hi', 5, 'xy'), ('', 3, 'a'), (NULL, 5, 'x'), ('hi', 0, 'x'), ('hi', -1, 'x'), ('hi', NULL, 'x'), (NULL, NULL, 'x'), ('hi', 5, NULL), ('hi', 5, ''), ('', 3, ''), ('hi', -100, 'x'), (NULL, NULL, NULL), ('"hi', 7, '"x'), ('café', 7, '中文'), ('é', 5, '🙂')
+INSERT INTO test_lpad VALUES ('hi', 5, 'x'), ('hello', 3, 'x'), ('hi', 5, 'xy'), ('', 3, 'a'), ('', 0, 'x'), (NULL, 5, 'x'), ('hi', 0, 'x'), ('hi', -1, 'x'), ('hi', NULL, 'x'), (NULL, NULL, 'x'), ('hi', 5, NULL), ('hi', 5, ''), ('', 3, ''), ('hi', -100, 'x'), (NULL, NULL, NULL), ('"hi', 7, '"x'), ('café', 7, '中文'), ('é', 5, '🙂')
 
 -- Column padding runs through the codegen dispatcher (issue #5579).
-query
+query expect_dispatch(lpad)
 SELECT lpad(s, len, pad) FROM test_lpad
 
-query
+query expect_dispatch(lpad)
 SELECT lpad(s, 5, pad) FROM test_lpad
 
-query
+query expect_dispatch(lpad)
 SELECT lpad('hi', len, pad) FROM test_lpad
 
-query
+query expect_dispatch(lpad)
 SELECT lpad('hi', len, 'xy') FROM test_lpad
 
-query
+query expect_dispatch(lpad)
 SELECT lpad('hi', len) FROM test_lpad
 
-query
+query expect_native(lpad)
 SELECT lpad(s, len) FROM test_lpad
 
 -- column + column + literal
-query
+query expect_native(lpad)
 SELECT lpad(s, len, 'x') FROM test_lpad
 
+query expect_native(lpad)
+SELECT lpad(s, len, 'xy') FROM test_lpad
+
 -- column + literal + literal
-query
+query expect_native(lpad)
 SELECT lpad(s, 5, 'x') FROM test_lpad
 
 -- literal + literal + literal
-query
+query expect_dispatch(lpad)
 SELECT lpad('hi', 5, 'x'), lpad('hello', 3, 'x'), lpad('', 3, 'a'), lpad(NULL, 5, 'x')
+
+query expect_dispatch(lpad)
+SELECT lpad('hi', 5, 'xy') FROM test_lpad
diff --git a/spark/src/test/resources/sql-tests/expressions/string/string_lpad_fallback.sql b/spark/src/test/resources/sql-tests/expressions/string/string_lpad_fallback.sql
index 32c476379d..76020ae374 100644
--- a/spark/src/test/resources/sql-tests/expressions/string/string_lpad_fallback.sql
+++ b/spark/src/test/resources/sql-tests/expressions/string/string_lpad_fallback.sql
@@ -21,20 +21,23 @@ statement
 CREATE TABLE test_lpad_fallback(s string, len int, pad string) USING parquet
 
 statement
-INSERT INTO test_lpad_fallback VALUES ('hi', 5, 'xy'), ('hello', 3, 'x'), (NULL, NULL, NULL)
+INSERT INTO test_lpad_fallback VALUES ('hi', 5, 'xy'), ('hello', 3, 'x'), ('', 3, 'a'), ('', 0, 'x'), ('hi', 5, ''), (NULL, 5, 'x'), ('hi', NULL, 'x'), ('hi', 5, NULL), (NULL, NULL, NULL)
 
-query expect_fallback(spark.comet.exec.scalaUDF.codegen.enabled)
+query expect_fallback(lpad: spark.comet.exec.scalaUDF.codegen.enabled=false)
 SELECT lpad(s, len, pad) FROM test_lpad_fallback
 
-query expect_fallback(spark.comet.exec.scalaUDF.codegen.enabled)
+query expect_fallback(lpad: spark.comet.exec.scalaUDF.codegen.enabled=false)
 SELECT lpad('hi', len, 'xy') FROM test_lpad_fallback
 
-query expect_fallback(spark.comet.exec.scalaUDF.codegen.enabled)
+query expect_fallback(lpad: spark.comet.exec.scalaUDF.codegen.enabled=false)
 SELECT lpad('hi', 5, 'xy')
 
+query expect_fallback(lpad: spark.comet.exec.scalaUDF.codegen.enabled=false)
+SELECT lpad('hi', 5, 'xy') FROM test_lpad_fallback
+
 -- The native argument shapes do not require the dispatcher.
-query
+query expect_native(lpad)
 SELECT lpad(s, len, 'xy') FROM test_lpad_fallback
 
-query
+query expect_native(lpad)
 SELECT lpad(s, len) FROM test_lpad_fallback
diff --git a/spark/src/test/resources/sql-tests/expressions/string/string_rpad.sql b/spark/src/test/resources/sql-tests/expressions/string/string_rpad.sql
index a5f9951273..6f24386736 100644
--- a/spark/src/test/resources/sql-tests/expressions/string/string_rpad.sql
+++ b/spark/src/test/resources/sql-tests/expressions/string/string_rpad.sql
@@ -15,39 +15,47 @@
 -- specific language governing permissions and limitations
 -- under the License.
 
+-- Config: spark.comet.exec.scalaUDF.codegen.enabled=true
+
 statement
 CREATE TABLE test_rpad(s string, len int, pad string) USING parquet
 
 statement
-INSERT INTO test_rpad VALUES ('hi', 5, 'x'), ('hello', 3, 'x'), ('hi', 5, 'xy'), ('', 3, 'a'), (NULL, 5, 'x'), ('hi', 0, 'x'), ('hi', -1, 'x'), ('hi', NULL, 'x'), (NULL, NULL, 'x'), ('hi', 5, NULL), ('hi', 5, ''), ('', 3, ''), ('hi', -100, 'x'), (NULL, NULL, NULL), ('"hi', 7, '"x'), ('café', 7, '中文'), ('é', 5, '🙂')
+INSERT INTO test_rpad VALUES ('hi', 5, 'x'), ('hello', 3, 'x'), ('hi', 5, 'xy'), ('', 3, 'a'), ('', 0, 'x'), (NULL, 5, 'x'), ('hi', 0, 'x'), ('hi', -1, 'x'), ('hi', NULL, 'x'), (NULL, NULL, 'x'), ('hi', 5, NULL), ('hi', 5, ''), ('', 3, ''), ('hi', -100, 'x'), (NULL, NULL, NULL), ('"hi', 7, '"x'), ('café', 7, '中文'), ('é', 5, '🙂')
 
 -- Column padding runs through the codegen dispatcher (issue #5579).
-query
+query expect_dispatch(rpad)
 SELECT rpad(s, len, pad) FROM test_rpad
 
-query
+query expect_dispatch(rpad)
 SELECT rpad(s, 5, pad) FROM test_rpad
 
-query
+query expect_dispatch(rpad)
 SELECT rpad('hi', len, pad) FROM test_rpad
 
-query
+query expect_dispatch(rpad)
 SELECT rpad('hi', len, 'xy') FROM test_rpad
 
-query
+query expect_dispatch(rpad)
 SELECT rpad('hi', len) FROM test_rpad
 
-query
+query expect_native(rpad)
 SELECT rpad(s, len) FROM test_rpad
 
 -- column + column + literal
-query
+query expect_native(rpad)
 SELECT rpad(s, len, 'x') FROM test_rpad
 
+query expect_native(rpad)
+SELECT rpad(s, len, 'xy') FROM test_rpad
+
 -- column + literal + literal
-query
+query expect_native(rpad)
 SELECT rpad(s, 5, 'x') FROM test_rpad
 
 -- literal + literal + literal
-query
+query expect_dispatch(rpad)
 SELECT rpad('hi', 5, 'x'), rpad('hello', 3, 'x'), rpad('', 3, 'a'), rpad(NULL, 5, 'x')
+
+query expect_dispatch(rpad)
+SELECT rpad('hi', 5, 'xy') FROM test_rpad
diff --git a/spark/src/test/resources/sql-tests/expressions/string/string_rpad_fallback.sql b/spark/src/test/resources/sql-tests/expressions/string/string_rpad_fallback.sql
index 8ac5bb36ba..c2c37b7970 100644
--- a/spark/src/test/resources/sql-tests/expressions/string/string_rpad_fallback.sql
+++ b/spark/src/test/resources/sql-tests/expressions/string/string_rpad_fallback.sql
@@ -21,20 +21,23 @@ statement
 CREATE TABLE test_rpad_fallback(s string, len int, pad string) USING parquet
 
 statement
-INSERT INTO test_rpad_fallback VALUES ('hi', 5, 'xy'), ('hello', 3, 'x'), (NULL, NULL, NULL)
+INSERT INTO test_rpad_fallback VALUES ('hi', 5, 'xy'), ('hello', 3, 'x'), ('', 3, 'a'), ('', 0, 'x'), ('hi', 5, ''), (NULL, 5, 'x'), ('hi', NULL, 'x'), ('hi', 5, NULL), (NULL, NULL, NULL)
 
-query expect_fallback(spark.comet.exec.scalaUDF.codegen.enabled)
+query expect_fallback(rpad: spark.comet.exec.scalaUDF.codegen.enabled=false)
 SELECT rpad(s, len, pad) FROM test_rpad_fallback
 
-query expect_fallback(spark.comet.exec.scalaUDF.codegen.enabled)
+query expect_fallback(rpad: spark.comet.exec.scalaUDF.codegen.enabled=false)
 SELECT rpad('hi', len, 'xy') FROM test_rpad_fallback
 
-query expect_fallback(spark.comet.exec.scalaUDF.codegen.enabled)
+query expect_fallback(rpad: spark.comet.exec.scalaUDF.codegen.enabled=false)
 SELECT rpad('hi', 5, 'xy')
 
+query expect_fallback(rpad: spark.comet.exec.scalaUDF.codegen.enabled=false)
+SELECT rpad('hi', 5, 'xy') FROM test_rpad_fallback
+
 -- The native argument shapes do not require the dispatcher.
-query
+query expect_native(rpad)
 SELECT rpad(s, len, 'xy') FROM test_rpad_fallback
 
-query
+query expect_native(rpad)
 SELECT rpad(s, len) FROM test_rpad_fallback
diff --git a/spark/src/test/scala/org/apache/comet/CometStringExpressionSuite.scala b/spark/src/test/scala/org/apache/comet/CometStringExpressionSuite.scala
index c58403487a..f5d594d1af 100644
--- a/spark/src/test/scala/org/apache/comet/CometStringExpressionSuite.scala
+++ b/spark/src/test/scala/org/apache/comet/CometStringExpressionSuite.scala
@@ -46,53 +46,6 @@ class CometStringExpressionSuite extends CometTestBase with CometCodegenAssertio
     testStringPadding("rpad")
   }
 
-  for ((function, expressionName) <- Seq("lpad" -> "StringLPad", "rpad" -> "StringRPad")) {
-    test(s"$function dispatches unsupported argument shapes (issue #5579)") {
-      val data: Seq[(String, Option[Int], String)] = Seq(
-        ("hi", Some(5), "xy"),
-        ("hello", Some(3), "x"),
-        ("", Some(3), "a"),
-        ("hi", Some(5), ""),
-        (null, Some(5), "x"),
-        ("hi", None, "x"),
-        ("hi", Some(5), null),
-        (null, None, null))
-      withParquetTable(data, "tbl") {
-        withSQLConf(
-          SQLConf.OPTIMIZER_EXCLUDED_RULES.key ->
-            "org.apache.spark.sql.catalyst.optimizer.ConstantFolding") {
-          for (allowIncompatible <- Seq("false", "true")) {
-            withSQLConf(
-              CometConf.getExprAllowIncompatConfigKey(expressionName) -> allowIncompatible) {
-              for (query <- Seq(
-                  s"SELECT $function(_1, _2, _3) FROM tbl",
-                  s"SELECT $function('hi', _2, 'xy') FROM tbl",
-                  s"SELECT $function('hi', 5, 'xy') FROM tbl")) {
-                assertCodegenRan {
-                  checkSparkAnswerAndOperator(query)
-                }
-              }
-            }
-          }
-        }
-      }
-    }
-
-    test(s"$function keeps supported argument shapes native") {
-      withParquetTable(Seq(("hi", 5), ("hello", 3), ("", 0)), "tbl") {
-        for (query <- Seq(
-            s"SELECT $function(_1, _2) FROM tbl",
-            s"SELECT $function(_1, _2, 'xy') FROM tbl")) {
-          CometScalaUDFCodegen.resetStats()
-          checkSparkAnswerAndOperator(query)
-          assert(
-            CometScalaUDFCodegen.stats().totalLookups == 0,
-            s"expected native execution for $query")
-        }
-      }
-    }
-  }
-
   test("lpad/rpad with NULL length") {
     // FuzzDataGenerator never generates NULL integers (#5389), so build the rows explicitly.
     // Spark's StringLPad/StringRPad are null-intolerant: a NULL length yields a NULL row.