Added a suppressed exception in cluster initialization (#3274)

Author: sazzad16

src/main/java/redis/clients/jedis/providers/ClusterConnectionProvider.java

@@ -15,7 +15,6 @@
 import redis.clients.jedis.ConnectionPool;
 import redis.clients.jedis.JedisClusterInfoCache;
 import redis.clients.jedis.exceptions.JedisClusterOperationException;
-import redis.clients.jedis.exceptions.JedisConnectionException;
 import redis.clients.jedis.exceptions.JedisException;
 
 public class ClusterConnectionProvider implements ConnectionProvider {
@@ -34,19 +33,30 @@ public ClusterConnectionProvider(Set<HostAndPort> clusterNodes, JedisClientConfi
   }
 
   private void initializeSlotsCache(Set<HostAndPort> startNodes, JedisClientConfig clientConfig) {
+    if (startNodes.isEmpty()) {
+      throw new JedisClusterOperationException("No nodes to initialize cluster slots cache.");
+    }
+
     ArrayList<HostAndPort> startNodeList = new ArrayList<>(startNodes);
     Collections.shuffle(startNodeList);
 
+    JedisException firstException = null;
     for (HostAndPort hostAndPort : startNodeList) {
       try (Connection jedis = new Connection(hostAndPort, clientConfig)) {
         cache.discoverClusterNodesAndSlots(jedis);
         return;
       } catch (JedisException e) {
+        if (firstException == null) {
+          firstException = e;
+        }
         // try next nodes
       }
     }
 
-    throw new JedisClusterOperationException("Could not initialize cluster slots cache.");
+    JedisClusterOperationException uninitializedException
+        = new JedisClusterOperationException("Could not initialize cluster slots cache.");
+    uninitializedException.addSuppressed(firstException);
+    throw uninitializedException;
   }
 
   @Override

src/test/java/redis/clients/jedis/JedisClusterWithoutSetupTest.java

@@ -1,13 +1,27 @@
 package redis.clients.jedis;
 
-import org.junit.Test;
+import static java.util.Collections.emptySet;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
 
+import org.junit.Test;
 import redis.clients.jedis.exceptions.JedisClusterOperationException;
 
 public class JedisClusterWithoutSetupTest {
 
-  @Test(expected = JedisClusterOperationException.class)
+  @Test
+  public void noStartNodes() {
+    JedisClusterOperationException operationException = assertThrows(
+        JedisClusterOperationException.class, () -> new JedisCluster(emptySet()));
+    assertEquals("No nodes to initialize cluster slots cache.", operationException.getMessage());
+    assertEquals(0, operationException.getSuppressed().length);
+  }
+
+  @Test
   public void uselessStartNodes() {
-    new JedisCluster(new HostAndPort("localhost", 7378));
+    JedisClusterOperationException operationException = assertThrows(
+        JedisClusterOperationException.class, () -> new JedisCluster(new HostAndPort("localhost", 7378)));
+    assertEquals("Could not initialize cluster slots cache.", operationException.getMessage());
+    assertEquals(1, operationException.getSuppressed().length);
   }
 }