Do we need this comment? The assertion message already explains the intent (e.g., “Expected at least 10 ConnectionCheckOutFailedEvents, but got …”).

The same as in: https://github.com/mongodb/mongo-java-driver/pull/1900/changes#r2908976631

This cleanup is currently conditional on the code above completing successfully. If an assertion or exception happens earlier, this teardown won’t run, which can leak state into subsequent tests.

We should move it this cleanup into @AfterEach/afterEach so it runs reliably regardless of how the test exits.

Instead of introducing a new anonymous listener with counters, we can reuse the existing test listener:

TestConnectionPoolListener connectionPoolListener = new TestConnectionPoolListener();

It already provides await helpers that double as assertions and helpers to assert that zero PoolClearedEvents happened, e.g.:

connectionPoolListener.waitForEvent(ConnectionPoolClearedEvent.class, 1, 110, SECONDS);

This keeps the test more concise and reuses established utilities for clarity/consistency.

Currently we attach SystemOverloadedError and RetryableError labels in the SDAM error-handling path (effectively only for DefaultServer). In load-balanced mode, SDAM isn’t involved: the LB code path invalidates the pool directly (e.g., connectionPool.invalidate(serviceId, generation)), so the labeling logic is bypassed.

This means users running the driver in LB mode (behind an NLB) can still hit network errors, TLS handshake failures, timeouts during connection establishment or hello, but won’t get the labels.

However, these labels are a CMAP requirement, not SDAM. The CMAP spec states: “The pool MUST add the error labels SystemOverloadedError and RetryableError to network errors or network timeouts it encounters during the connection establishment or the hello message.”

Since this is defined as a pool behavior (topology-agnostic), it seems we should implement the labeling in the connection pool layer so it applies consistently in both default and load-balanced modes.

Currently we don’t distinguish DNS lookup failures (UnknownHostException) from other connection-establishment network errors. As a result, a DNS failure goes through the generic path (same as connection reset/timeout) and gets SystemOverloadedError/RetryableError labels.

The CMAP spec excludes DNS failures from backpressure labeling: `“For errors that the driver can distinguish as never occurring due to server overload, such as DNS lookup failures […] the driver MUST NOT add backpressure error labels for these error types.”.

Proposed change: detect DNS failure by walking the exception cause chain for UnknownHostException (it’s wrapped as MongoSocketException from ServerAddressHelper.getSocketAddresses()), and when present, skipping backpressure label attachment so SDAM follows the normal path (clear the pool and mark the server Unknown).

In that case, we should add coverage to assert that labeling and pool clearing behaviour. If the driver ever changes the wrapper exception type MongoSocketException (or stops wrapping UnknownHostException this way) and starts adding labels the test should fail.