IGNITE-27206 Fixed flaky the testRemovedConnectionMetrics test (#12545)

Author: Vladsz83

modules/core/src/test/java/org/apache/ignite/spi/communication/tcp/CommunicationConnectionPoolMetricsTest.java

@@ -79,6 +79,9 @@ public class CommunicationConnectionPoolMetricsTest extends GridCommonAbstractTe
     /** */
     private volatile long maxConnIdleTimeout = TcpCommunicationSpi.DFLT_IDLE_CONN_TIMEOUT;
 
+    /** */
+    private int ackSendThreshold = TcpCommunicationSpi.DFLT_ACK_SND_THRESHOLD;
+
     /** */
     private volatile int createClientDelay;
 
@@ -126,6 +129,7 @@ public static Collection<Object[]> params() {
         communicationSpi.setConnectionsPerNode(connsPerNode)
             .setUsePairedConnections(pairedConns)
             .setIdleConnectionTimeout(maxConnIdleTimeout)
+            .setAckSendThreshold(ackSendThreshold)
             .setMessageQueueLimit(msgQueueLimit);
 
         cfg.setCommunicationSpi(communicationSpi);
@@ -140,6 +144,10 @@ public static Collection<Object[]> params() {
     public void testRemovedConnectionMetrics() throws Exception {
         maxConnIdleTimeout = 500;
 
+        // Prevents keeping connections idle by lazy sending of the unacknowledged messages.
+        if (pairedConns)
+            ackSendThreshold = 1;
+
         Ignite srvr = startGridsMultiThreaded(2);
         Ignite cli = startClientGrid(G.allGrids().size());