fix(clustered pubsub): check that client.isOpen before calling client.disconnect() when unsubscribing (#2687)

* Confirm the client isOpen before disconnecting

* Write tests

* fix tests

* fix tests

---------

Co-authored-by: Leibale Eidelman <me@leibale.com>

Author: BrentLayne

packages/client/lib/cluster/cluster-slots.ts

@@ -562,7 +562,7 @@ export default class RedisClusterSlots<
         const client = await this.getPubSubClient();
         await unsubscribe(client);
 
-        if (!client.isPubSubActive) {
+        if (!client.isPubSubActive && client.isOpen) {
             await client.disconnect();
             this.pubSubNode = undefined;
         }
@@ -613,7 +613,7 @@ export default class RedisClusterSlots<
         const client = await master.pubSubClient;
         await unsubscribe(client);
 
-        if (!client.isPubSubActive) {
+        if (!client.isPubSubActive && client.isOpen) {
             await client.disconnect();
             master.pubSubClient = undefined;
         }

packages/client/lib/cluster/index.spec.ts

@@ -235,6 +235,18 @@ describe('Cluster', () => {
 
             assert.equal(cluster.pubSubNode, undefined);
         }, GLOBAL.CLUSTERS.OPEN);
+        
+        testUtils.testWithCluster('concurrent UNSUBSCRIBE does not throw an error (#2685)', async cluster => {
+            const listener = spy();
+            await Promise.all([
+                cluster.subscribe('1', listener),
+                cluster.subscribe('2', listener)
+            ]);
+            await Promise.all([
+                cluster.unsubscribe('1', listener),
+                cluster.unsubscribe('2', listener)
+            ]);
+        }, GLOBAL.CLUSTERS.OPEN);
 
         testUtils.testWithCluster('psubscribe & punsubscribe', async cluster => {
             const listener = spy();
@@ -323,6 +335,21 @@ describe('Cluster', () => {
             minimumDockerVersion: [7]
         });
 
+        testUtils.testWithCluster('concurrent SUNSUBCRIBE does not throw an error (#2685)', async cluster => {
+            const listener = spy();
+            await Promise.all([
+                await cluster.sSubscribe('1', listener),
+                await cluster.sSubscribe('2', listener)
+            ]);
+            await Promise.all([
+                cluster.sUnsubscribe('1', listener),
+                cluster.sUnsubscribe('2', listener)
+            ]);
+        }, {
+            ...GLOBAL.CLUSTERS.OPEN,
+            minimumDockerVersion: [7]
+        });
+
         testUtils.testWithCluster('should handle sharded-channel-moved events', async cluster => {
             const SLOT = 10328,
                 migrating = cluster.slots[SLOT].master,