Adds test for recipient registry

Signed-off-by: Darshit Chanpura <[email protected]>

server/src/main/java/org/opensearch/accesscontrol/resources/RecipientTypeRegistry.java

@@ -26,7 +26,7 @@ public static void registerRecipientType(String key, RecipientType recipientType
     public static RecipientType fromValue(String value) {
         RecipientType type = REGISTRY.get(value);
         if (type == null) {
-            throw new IllegalArgumentException("Unknown RecipientType: " + value);
+            throw new IllegalArgumentException("Unknown RecipientType: " + value + ". Must be 1 of these: " + REGISTRY.values());
         }
         return type;
     }

server/src/test/java/org/opensearch/accesscontrol/resources/RecipientTypeRegistryTests.java

@@ -0,0 +1,32 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.accesscontrol.resources;
+
+import org.opensearch.test.OpenSearchTestCase;
+import org.hamcrest.MatcherAssert;
+
+import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.is;
+
+public class RecipientTypeRegistryTests extends OpenSearchTestCase {
+
+    public void testFromValue() {
+        RecipientTypeRegistry.registerRecipientType("ble1", new RecipientType("ble1"));
+        RecipientTypeRegistry.registerRecipientType("ble2", new RecipientType("ble2"));
+
+        // Valid Value
+        RecipientType type = RecipientTypeRegistry.fromValue("ble1");
+        assertNotNull(type);
+        assertEquals("ble1", type.getType());
+
+        // Invalid Value
+        IllegalArgumentException exception = assertThrows(IllegalArgumentException.class, () -> RecipientTypeRegistry.fromValue("bleble"));
+        MatcherAssert.assertThat("Unknown RecipientType: bleble. Must be 1 of these: [ble1, ble2]", is(equalTo(exception.getMessage())));
+    }
+}