WebFilterChain delegation nested in Mono.defer()

Issue: SPR-15520

spring-web/src/main/java/org/springframework/web/server/handler/DefaultWebFilterChain.java

@@ -68,14 +68,16 @@ public class DefaultWebFilterChain implements WebFilterChain {
 
 	@Override
 	public Mono<Void> filter(ServerWebExchange exchange) {
-		if (this.index < this.filters.size()) {
-			WebFilter filter = this.filters.get(this.index);
-			WebFilterChain chain = new DefaultWebFilterChain(this, this.index + 1);
-			return filter.filter(exchange, chain);
-		}
-		else {
-			return this.handler.handle(exchange);
-		}
+		return Mono.defer(() -> {
+			if (this.index < this.filters.size()) {
+				WebFilter filter = this.filters.get(this.index);
+				WebFilterChain chain = new DefaultWebFilterChain(this, this.index + 1);
+				return filter.filter(exchange, chain);
+			}
+			else {
+				return this.handler.handle(exchange);
+			}
+		});
 	}
 
 }

spring-web/src/test/java/org/springframework/web/server/handler/FilteringWebHandlerTests.java

@@ -104,7 +104,7 @@ public class FilteringWebHandlerTests {
 
 		new FilteringWebHandler(targetHandler, Collections.singletonList(filter))
 				.handle(MockServerHttpRequest.get("/").toExchange())
-				.block(Duration.ZERO);
+				.block(Duration.ofSeconds(5));
 
 		assertTrue(filter.invoked());
 		assertTrue(targetHandler.invoked());
@@ -170,7 +170,7 @@ public class FilteringWebHandlerTests {
 		}
 
 		private Mono<String> doAsyncWork() {
-			return Mono.just("123");
+			return Mono.delay(Duration.ofMillis(100L)).map(l -> "123");
 		}
 	}