adding unit test to address comments

Signed-off-by: Dhrubo Saha <dhrubo@amazon.com>

plugin/src/test/java/org/opensearch/ml/rest/RestMLRemoteInferenceIT.java

@@ -17,6 +17,7 @@
 import org.junit.Before;
 import org.junit.Ignore;
 import org.junit.Rule;
+import org.junit.Test;
 import org.junit.rules.ExpectedException;
 import org.opensearch.client.Response;
 import org.opensearch.client.ResponseException;
@@ -104,6 +105,30 @@ private static String maskSensitiveInfo(String input) {
         return input.replaceAll(regex, "\"credential\": \"***\"");
     }
 
+    @Test
+    public void testMaskSensitiveInfo_withCredential() {
+        String input = "{\"credential\":{\"username\":\"admin\",\"password\":\"secret\"}}";
+        String expectedOutput = "{\"credential\": \"***\"}";
+        String actualOutput = maskSensitiveInfo(input);
+        assertEquals(expectedOutput, actualOutput);
+    }
+
+    @Test
+    public void testMaskSensitiveInfo_noCredential() {
+        String input = "{\"otherInfo\":\"someValue\"}";
+        String expectedOutput = "{\"otherInfo\":\"someValue\"}";
+        String actualOutput = maskSensitiveInfo(input);
+        assertEquals(expectedOutput, actualOutput);
+    }
+
+    @Test
+    public void testMaskSensitiveInfo_emptyInput() {
+        String input = "";
+        String expectedOutput = "";
+        String actualOutput = maskSensitiveInfo(input);
+        assertEquals(expectedOutput, actualOutput);
+    }
+
     public void testSearchConnectors_beforeCreation() throws IOException {
         String searchEntity = "{\n" + "  \"query\": {\n" + "    \"match_all\": {}\n" + "  },\n" + "  \"size\": 1000\n" + "}";
         Response response = TestHelper