The Java unified test runner (driver-sync/.../UnifiedTest.java:423-451) handles expectEvents with eventType: sdam by partitioning expected events into two buckets: topology vs everything else. The "everything
else" bucket is then asserted against TestServerMonitorListener.getEvents(), which only captures heartbeat events.

ServerDescriptionChangedEvent is captured by a separate listener, TestServerListener (reachable via entities.getServerListener(clientId).getServerDescriptionChangedEvents()), which the runner never consults
for eventType: sdam. As a result, any spec test that places a serverDescriptionChangedEvent inside an eventType: sdam expectEvents block always compares expected-non-empty against actual-empty and fails with
"Number of events must be the same. expected:<N> but was:<0>".

First test that exercises this path: testing/resources/specifications/source/server-discovery-and-monitoring/tests/unified/backpressure-server-description-unchanged-on-min-pool-size-population-error.yml
(introduced by DRIVERS-3218). This test asserts the CMAP backpressure invariant "the server description is not changed on handshake error during minPoolSize population" via a single expectEvents → eventType:
sdam → [{ serverDescriptionChangedEvent: {} }]. It's currently skipped in Java under JAVA-5949 (pending this fix) via UnifiedTestModifications.java.

Peer-driver comparison:

• Node.js: single sdamEvents[] array on UnifiedMongoClient, populated by registering listeners for all SDAM events directly on the MongoClient (test/tools/unified-spec-runner/entities.ts, NODE-4534,
  2022-08-24). No gap.
• .NET: single per-client EventCapturer with .Capture<ServerDescriptionChangedEvent>() + heartbeat types; UnifiedEventMatcher.FilterEventsBySetType(events, "sdam") partitions by bucket
  (tests/.../UnifiedEventMatcher.cs, CSHARP-4227, 2023-02-25). No gap.

Java is the only outlier; the bug is long-standing (predates the backpressure spec) but only now exercised by a committed spec test.

Repro:
1. Remove the skip for backpressure-server-description-unchanged-on-min-pool-size-population-error in UnifiedTestModifications.java.
2. ./gradlew :driver-sync:test --tests "UnifiedServerDiscoveryAndMonitoringTest*backpressure-server-description-unchanged" on a standalone 7.0+ server.
3. Observe: AssertionError: Number of events must be the same. expected:<1> but was:<0>.