Added test case to cover future regressions of this change

test/integration/test-pool-release-idle-connection-replicate.test.cjs

@@ -0,0 +1,69 @@
+'use strict';
+const createPool = require('../common.test.cjs').createPool;
+const { assert } = require('poku');
+
+/**
+ * This test case tests the scenario where released connections are not
+ * being destroyed after the idle timeout has passed, to do this we setup
+ * a pool with a connection limit of 3, and a max idle of 2, and an idle
+ * timeout of 1 second. We then create 3 connections, and release them
+ * after 1 second, we then check that the pool has 0 connections, and 0
+ * free connections.
+ *
+ * @see https://github.com/sidorares/node-mysql2/issues/3020
+ */
+
+/**
+ * This test case
+ */
+const pool = new createPool({
+  connectionLimit: 3,
+  maxIdle: 2,
+  idleTimeout: 1000,
+});
+
+/**
+ * Create the first connection and ensure it's in the pool as expected
+ */
+pool.getConnection((err1, connection1) => {
+  assert.ifError(err1);
+  assert.ok(connection1);
+
+  /**
+   * Create the second connection and ensure it's in the pool as expected
+   */
+  pool.getConnection((err2, connection2) => {
+    assert.ifError(err2);
+    assert.ok(connection2);
+
+    /**
+     * Create the third connection and ensure it's in the pool as expected
+     */
+    pool.getConnection((err3, connection3) => {
+      assert.ifError(err3);
+      assert.ok(connection3);
+
+      /**
+       * Release all the connections
+       */
+      connection1.release();
+      connection2.release();
+      connection3.release();
+
+      /**
+       * After the idle timeout has passed, check that all items in the in the pool
+       * that have been released are destroyed as expected.
+       */
+      setTimeout(() => {
+        assert(
+          pool._allConnections.length === 0,
+          `Expected all connections to be closed, but found ${pool._allConnections.length}`,
+        );
+        assert(
+          pool._freeConnections.length === 0,
+          `Expected all free connections to be closed, but found ${pool._freeConnections.length}`,
+        );
+      }, 5000);
+    });
+  });
+});