Add unit tests for JetStreamMessageBrokerFactory ServiceLoader discovery

Assisted-By: Claude Code

Author: sonus21

rqueue-nats/src/test/java/com/github/sonus21/rqueue/nats/JetStreamMessageBrokerFactoryTest.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) 2024-2026 Sonu Kumar
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * You may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ */
+package com.github.sonus21.rqueue.nats;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.github.sonus21.rqueue.core.spi.MessageBrokerFactory;
+import com.github.sonus21.rqueue.core.spi.MessageBrokerLoader;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.ServiceLoader;
+import org.junit.jupiter.api.Test;
+
+/** ServiceLoader and configuration-parsing tests for {@link JetStreamMessageBrokerFactory}. */
+@NatsUnitTest
+class JetStreamMessageBrokerFactoryTest {
+
+  /** Use a port that isn't bound; jnats should fail fast trying to connect. */
+  private static Map<String, String> unreachableConfig() {
+    Map<String, String> cfg = new HashMap<>();
+    cfg.put("rqueue.nats.url", "nats://127.0.0.1:1");
+    return cfg;
+  }
+
+  @Test
+  void name_isLowercaseNats() {
+    assertEquals("nats", new JetStreamMessageBrokerFactory().name());
+  }
+
+  @Test
+  void serviceLoader_findsJetStreamFactory() {
+    JetStreamMessageBrokerFactory found = null;
+    for (MessageBrokerFactory f : ServiceLoader.load(MessageBrokerFactory.class)) {
+      if ("nats".equals(f.name()) && f instanceof JetStreamMessageBrokerFactory) {
+        found = (JetStreamMessageBrokerFactory) f;
+        break;
+      }
+    }
+    assertNotNull(found, "ServiceLoader did not discover JetStreamMessageBrokerFactory");
+  }
+
+  @Test
+  void create_withUnreachableUrl_throwsRqueueNatsException() {
+    JetStreamMessageBrokerFactory factory = new JetStreamMessageBrokerFactory();
+    RqueueNatsException ex =
+        assertThrows(RqueueNatsException.class, () -> factory.create(unreachableConfig()));
+    // message should reference NATS and the URL so failures are debuggable
+    String msg = ex.getMessage();
+    assertNotNull(msg);
+    assertTrue(msg.toLowerCase().contains("nats"), "message should mention NATS: " + msg);
+    assertTrue(msg.contains("127.0.0.1:1"), "message should include URL: " + msg);
+  }
+
+  @Test
+  void create_withNullConfig_throwsNpe() {
+    JetStreamMessageBrokerFactory factory = new JetStreamMessageBrokerFactory();
+    assertThrows(NullPointerException.class, () -> factory.create(null));
+  }
+
+  @Test
+  void messageBrokerLoader_load_natsBackend_routesToJetStreamFactory() {
+    // Same exception expected as direct factory.create() since URL is unreachable.
+    RqueueNatsException ex =
+        assertThrows(
+            RqueueNatsException.class, () -> MessageBrokerLoader.load("nats", unreachableConfig()));
+    assertTrue(ex.getMessage().toLowerCase().contains("nats"));
+  }
+
+  @Test
+  void messageBrokerLoader_load_unknownBackend_throwsIAE() {
+    IllegalArgumentException ex =
+        assertThrows(
+            IllegalArgumentException.class, () -> MessageBrokerLoader.load("nope", new HashMap<>()));
+    assertTrue(
+        ex.getMessage().contains("No MessageBrokerFactory found"),
+        "expected 'No MessageBrokerFactory found' in message but was: " + ex.getMessage());
+  }
+}