fix(pooling): make active-connection assertions race-free (#103)

* fix(pooling): make active-connection assertions race-free

box.stat.net().CONNECTIONS.current is updated asynchronously by the IProto
worker, so reading it once right after starting clients can return a stale
value and flake ConnectionPoolReconnectsTest. Replace the single read in
BasePoolTest#getActiveConnectionsCount with a bounded Lua poll that waits
until the counter stops changing, and add waitForActiveConnections helper
for tests that need to assert a specific count.

Author: dkasimovskiy

CHANGELOG.md

@@ -6,12 +6,21 @@
 
 - Add `tarantool-spring-data-40` module with support for Spring Boot 4.0.x and Spring Data 4.0.x
 
+### Bug fixes
+
+- Fix flaky `ConnectionPoolReconnectsTest` assertions on active connection count by polling 
+  `box.stat.net().CONNECTIONS.current` from Lua until it holds the same value across 
+  5 consecutive reads at 100ms intervals, instead of a single read that races with the IProto worker
+
 ### Testcontainers
 
 - Add TQE 3.x (message-queue-ee 3.x) integration on top of the
   existing TQE 2.x support; consolidate the TQE 2.x / 3.x test
   surface into a single parameterized suite.
-- Add constructor/builder parameters to supply the initial Lua script as a string or as a file path, and optional additional script paths copied into the container data directory (`Tarantool2Container`, `CartridgeClusterContainer`, `VshardClusterContainer`); simplify bundled `server.lua` accordingly.
+- Add constructor/builder parameters to supply the initial Lua script as a string or as a file path, 
+  and optional additional script paths copied into the container data directory 
+  (`Tarantool2Container`, `CartridgeClusterContainer`, `VshardClusterContainer`); 
+  simplify bundled `server.lua` accordingly.
 - Upgrade TQE to v3.5.0.
 - Extract `ObjectMapper` to a static field in the test `tdg.Utils` helper to avoid recreating it on every `sendUsers`/`getUsers` call.
 
@@ -21,8 +30,10 @@
 
 ### Documentation
 
-- Document supported Java types for Tarantool data mapping in `tuple_pojo_mapping` docs (RU/EN), including Tarantool extension types (`decimal`, `uuid`, `datetime`, `interval`, `tuple`) and related mapping notes.
-- Document Jackson MsgPack deserialization: integers, `bin`/`str` vs `byte[]`/`String`, floating-point vs `decimal`; reference `jackson-dataformat-msgpack` for defaults and type coercion.
+- Document supported Java types for Tarantool data mapping in `tuple_pojo_mapping` docs (RU/EN), 
+  including Tarantool extension types (`decimal`, `uuid`, `datetime`, `interval`, `tuple`) and related mapping notes.
+- Document Jackson MsgPack deserialization: integers, `bin`/`str` vs `byte[]`/`String`, floating-point vs `decimal`; 
+  reference `jackson-dataformat-msgpack` for defaults and type coercion.
 
 ### Dependencies
 - Updated dependencies:

tarantool-pooling/src/test/java/io/tarantool/pool/integration/BasePoolTest.java

@@ -15,6 +15,7 @@
 import java.util.concurrent.CompletionException;
 import java.util.concurrent.ThreadLocalRandom;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 import static org.junit.jupiter.api.Assertions.fail;
 import io.micrometer.core.instrument.Counter;
@@ -93,10 +94,25 @@ protected void execLua(TarantoolContainer<?> container, String command) {
 
   protected int getActiveConnectionsCount(TarantoolContainer<?> tt) {
     try {
-      List<? extends Object> result =
-          TarantoolContainerClientHelper.executeCommandDecoded(
-              tt, "return box.stat.net().CONNECTIONS.current");
-      return (Integer) result.get(0) - 1;
+      // IProto worker updates CONNECTIONS.current asynchronously; require 5 consecutive equal
+      // reads at 100ms intervals before trusting the value (100 iters = 10s safety net).
+      String lua =
+          "local last = box.stat.net().CONNECTIONS.current;"
+              + " local stable = 1;"
+              + " for i = 1, 100 do"
+              + " require('fiber').sleep(0.1);"
+              + " local cur = box.stat.net().CONNECTIONS.current;"
+              + " if cur == last then"
+              + " stable = stable + 1;"
+              + " if stable >= 5 then return cur - 1 end;"
+              + " else"
+              + " last = cur;"
+              + " stable = 1;"
+              + " end;"
+              + " end;"
+              + " return last - 1";
+      List<? extends Object> result = TarantoolContainerClientHelper.executeCommandDecoded(tt, lua);
+      return (Integer) result.get(0);
     } catch (Exception e) {
       throw new RuntimeException(e);
     }
@@ -106,6 +122,10 @@ protected int getActiveConnectionsCountDelta(TarantoolContainer<?> tt, int basel
     return getActiveConnectionsCount(tt) - baseline;
   }
 
+  protected void waitForActiveConnections(TarantoolContainer<?> tt, int expected) {
+    assertEquals(expected, getActiveConnectionsCount(tt));
+  }
+
   protected MeterRegistry createMetricsRegistry() {
     MeterRegistry metricsRegistry = new SimpleMeterRegistry();
     LongTaskTimer.builder("request.timer")

tarantool-pooling/src/test/java/io/tarantool/pool/integration/ConnectionPoolReconnectsTest.java

@@ -77,7 +77,7 @@ public void testReconnectAfterNodeFailure() throws Exception {
     assertTrue(pool.hasAvailableClients());
     List<IProtoClient> clients = getConnects(pool, "node-a", count1);
     assertTrue(pingClients(clients));
-    assertEquals(count1, getActiveConnectionsCount(tt));
+    waitForActiveConnections(tt, count1);
 
     tt.stop();
     Thread.sleep(1000);
@@ -110,7 +110,7 @@ public void testReconnectAfterNodeFailure() throws Exception {
         });
 
     assertTrue(pingClients(clients));
-    assertEquals(count1, getActiveConnectionsCount(tt));
+    waitForActiveConnections(tt, count1);
 
     assertEquals(count1, metricsRegistry.get("pool.size").gauge().value());
     assertEquals(count1, metricsRegistry.get("pool.available").gauge().value());