fix anonymizer test

Signed-off-by: Jialiang Liang <jiallian@amazon.com>

Author: RyanL1997

ppl/src/main/java/org/opensearch/sql/ppl/parser/AstBuilder.java

@@ -967,6 +967,7 @@ public UnresolvedPlan visitRegexCommand(OpenSearchPPLParser.RegexCommandContext
     return new Regex(field, negated, pattern);
   }
 
+  @Override
   public UnresolvedPlan visitRexCommand(OpenSearchPPLParser.RexCommandContext ctx) {
     UnresolvedExpression field = internalVisitExpression(ctx.rexExpr().field);
     Literal pattern = (Literal) internalVisitExpression(ctx.rexExpr().pattern);

ppl/src/main/java/org/opensearch/sql/ppl/utils/PPLQueryDataAnonymizer.java

@@ -460,13 +460,11 @@ public String visitRex(Rex node, String context) {
     String pattern = "\"" + node.getPattern().toString() + "\"";
     StringBuilder command = new StringBuilder();
 
-    // Build the base command
     command.append(
         String.format(
             "%s | rex field=%s mode=%s %s",
             child, field, node.getMode().toString().toLowerCase(), pattern));
 
-    // Add optional parameters
     if (node.getMaxMatch().isPresent()) {
       command.append(" max_match=").append(node.getMaxMatch().get());
     }

ppl/src/test/java/org/opensearch/sql/ppl/utils/PPLQueryDataAnonymizerTest.java

@@ -531,11 +531,13 @@ public void testRegex() {
 
   @Test
   public void testRexCommand() {
+    when(settings.getSettingValue(Key.PPL_REX_MAX_MATCH_LIMIT)).thenReturn(10);
+
     assertEquals(
-        "source=t | rex field=message mode=extract \"(?<user>[A-Z]+)\"",
+        "source=t | rex field=message mode=extract \"(?<user>[A-Z]+)\" max_match=1",
         anonymize("source=t | rex field=message \"(?<user>[A-Z]+)\""));
     assertEquals(
-        "source=t | rex field=lastname mode=extract \"(?<initial>^[A-Z])\" | fields +"
+        "source=t | rex field=lastname mode=extract \"(?<initial>^[A-Z])\" max_match=1 | fields +"
             + " lastname,initial",
         anonymize(
             "source=t | rex field=lastname \"(?<initial>^[A-Z])\" | fields lastname, initial"));