test(spanner): unflake ITBulkConnectionTest.testBulkCreateConnectionsMultiThreaded

[sakthivelmanii]

Root Cause

ITBulkConnectionTest.testBulkCreateConnectionsMultiThreaded submits 250 connection and query tasks across a 50-thread pool and calls executor.awaitTermination(10L, TimeUnit.SECONDS) without asserting its return value or waiting for the submitted task Futures. When initial Spanner client and metrics setup plus 250 connection handshakes exceed 10 seconds, awaitTermination returns false while worker threads still have open connections in flight, causing closeSpanner() in @AfterClass to fail with FAILED_PRECONDITION: There is/are 1 connection(s) still open. Close all connections before calling closeSpanner().

Fix

• Collect all submitted task Futures and assert assertNull(future.get()) to propagate any worker exception and ensure all connections are closed before test completion.
• Increase executor.awaitTermination timeout from 10 seconds to 60 seconds and assert assertTrue(executor.awaitTermination(60L, TimeUnit.SECONDS)).

[gemini-code-assist]

Code Review

This pull request updates the multi-threaded bulk connection creation test in ITBulkConnectionTest.java to track the submitted tasks using Future objects. It now asserts that the executor terminates successfully within 60 seconds and verifies that each task completed without throwing an exception. There are no review comments, so I have no feedback to provide.

[olavloite]

nit: can we add a try-finally block to ensure that the executor is shut down also when the test fails, like this (and also use JUnit style assertions):

@Test
public void testBulkCreateConnectionsMultiThreaded() throws Exception {
  ExecutorService executor = Executors.newFixedThreadPool(50);
  try {
    List<Future<?>> futures = new ArrayList<>(NUMBER_OF_TEST_CONNECTIONS);
    for (int i = 0; i < NUMBER_OF_TEST_CONNECTIONS; i++) {
      futures.add(
          executor.submit(
              () -> {
                try (ITConnection connection = createConnection()) {
                  try (ResultSet resultSet = connection.executeQuery(Statement.of("select 1"))) {
                    assertTrue(resultSet.next());
                    assertNotNull(connection.getReadTimestamp());
                  }
                }
                return null;
              }));
    }
    executor.shutdown();
    assertTrue(
        "Executor did not terminate within timeout; active threads remain",
        executor.awaitTermination(60L, TimeUnit.SECONDS));
    for (Future<?> future : futures) {
      assertNull(future.get());
    }
  } finally {
    if (!executor.isTerminated()) {
      executor.shutdownNow();
      executor.awaitTermination(5L, TimeUnit.SECONDS);
    }
  }
  closeSpanner();
}

[sakthivelmanii]

Addressed in follow-up PR #14610.