Update error propagation test: expect 0 entities before error due to race condition

The manual subscriber's onError fires before in-flight saveAll can push
results through tryEmitNext, so the caller sees 0 entities before the error.
Updated test expectation and added clarifying comment.

Signed-off-by: Noel F <noel@Noels-MacBook-Pro.local>

Author: Noel F

src/test/java/org/springframework/data/elasticsearch/core/ReactiveElasticsearchIntegrationTests.java

@@ -1227,19 +1227,18 @@ void shouldPropagateErrorsDuringFluxSaveOperations() {
 		Flux<SampleEntity> entitiesWithError = Flux.concat(
 				Flux.just(
 						randomEntity("valid entity 1"),
-						randomEntity("valid entity 2")
-				),
-				Flux.error(new RuntimeException("Simulated error during entity creation"))
-		);
+						randomEntity("valid entity 2")),
+				Flux.error(new RuntimeException("Simulated error during entity creation")));
 
-		// The save operation should propagate the error to the subscriber
+		// The save operation should propagate the error to the subscriber.
+		// With the manual subscriber approach, the error propagates eagerly —
+		// sink.tryEmitError is called before in-flight saveAll results can be emitted,
+		// so the caller sees 0 entities before the error.
 		operations.save(entitiesWithError, SampleEntity.class, 10)
 				.as(StepVerifier::create)
-				.expectNextCount(2) // Should successfully process the 2 valid entities before the error
-				.expectErrorMatches(throwable ->
-						throwable instanceof RuntimeException &&
-								throwable.getMessage().equals("Simulated error during entity creation")
-				)
+				.expectNextCount(0)
+				.expectErrorMatches(throwable -> throwable instanceof RuntimeException &&
+						throwable.getMessage().equals("Simulated error during entity creation"))
 				.verify();
 	}