Refactor BaseConnectionPool empty method

CHANGELOG.md

@@ -18,6 +18,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Bumps `eslint-config-prettier` from 8.8.0 to 9.0.0
 ### Changed
 - Make handling of long numerals an option that is disabled by default ([#557](https://github.com/opensearch-project/opensearch-js/pull/557))
+- Refactor BaseConnectionPool empty method so that callback will always get called even when there is no connection ([#585](https://github.com/opensearch-project/opensearch-js/pull/585)) 
 ### Deprecated
 ### Removed
 ### Fixed

lib/pool/BaseConnectionPool.js

@@ -150,13 +150,14 @@ class BaseConnectionPool {
     let openConnections = this.size;
     this.connections.forEach((connection) => {
       connection.close(() => {
-        if (--openConnections === 0) {
-          this.connections = [];
-          this.size = this.connections.length;
-          callback();
-        }
+        openConnections--;
       });
     });
+    if (openConnections === 0) {
+      this.connections = [];
+      this.size = this.connections.length;
+      callback();
+    }
   }
 
   /**

test/unit/base-connection-pool.test.js

@@ -156,6 +156,14 @@ test('API', (t) => {
     t.end();
   });
 
+  t.test('empty with no connection', (t) => {
+    const pool = new BaseConnectionPool({ Connection });
+    t.equal(pool.connections.length, 0);
+    pool.empty();
+    t.equal(pool.size, 0);
+    t.end();
+  });
+
   t.test('urlToHost', (t) => {
     const pool = new BaseConnectionPool({ Connection });
     const url = 'http://localhost:9200';