Fix use CompletableFuture in DeferredResultReturnValueHandlerTest

See gh-22337

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/DeferredResultReturnValueHandlerTests.java

@@ -96,8 +96,8 @@ public class DeferredResultReturnValueHandlerTests {
 
 	@Test
 	public void completableFuture() throws Exception {
-		SettableListenableFuture<String> future = new SettableListenableFuture<>();
-		testHandle(future, CompletableFuture.class, () -> future.set("foo"), "foo");
+		CompletableFuture<String> future = new CompletableFuture<>();
+		testHandle(future, CompletableFuture.class, () -> future.complete("foo"), "foo");
 	}
 
 	@Test
@@ -115,9 +115,9 @@ public class DeferredResultReturnValueHandlerTests {
 
 	@Test
 	public void completableFutureWithError() throws Exception {
-		SettableListenableFuture<String> future = new SettableListenableFuture<>();
+		CompletableFuture<String> future = new CompletableFuture<>();
 		IllegalStateException ex = new IllegalStateException();
-		testHandle(future, CompletableFuture.class, () -> future.setException(ex), ex);
+		testHandle(future, CompletableFuture.class, () -> future.completeExceptionally(ex), ex);
 	}