test: add test for /issues/3148

Author: dstankovd

test/test-pool-releases-connections-gracefully.test.cjs

@@ -0,0 +1,41 @@
+'use strict';
+const createPool = require('../common.test.cjs').createPool;
+const { assert } = require('poku');
+
+/**
+ * This test case tests that the pool releases connections gracefully after the idle timeout has passed.
+ *
+ * @see https://github.com/sidorares/node-mysql2/issues/3148
+ */
+
+const pool = new createPool({
+  connectionLimit: 3,
+  maxIdle: 2,
+  idleTimeout: 1000,
+});
+
+let connection1Ended = false;
+let connection2Ended = false;
+let connection3Ended = false;
+
+pool.getConnection((_err1, connection1) => {
+  pool.getConnection((_err2, connection2) => {
+    pool.getConnection((_err3, connection3) => {
+      connection1.stream.on('end', () => (connection1Ended = true));
+      connection2.stream.on('end', () => (connection2Ended = true));
+      connection3.stream.on('end', () => (connection3Ended = true));
+
+      connection1.release();
+      connection2.release();
+      connection3.release();
+
+      setTimeout(() => {
+        assert(connection1Ended, 'connection1 should have ended');
+        assert(connection2Ended, 'connection2 should have ended');
+        assert(connection3Ended, 'connection3 should have ended');
+
+        pool.end();
+      }, 2000);
+    });
+  });
+});