Fix failing test

The onFailure callback and future.get() occur in different threads so
this change adds a latch to ensure we have both before asserting.

Issue: SPR-12887

spring-web/src/test/java/org/springframework/web/client/AsyncRestTemplateIntegrationTests.java

@@ -20,8 +20,10 @@ import java.net.URI;
 import java.nio.charset.Charset;
 import java.util.EnumSet;
 import java.util.Set;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
 
 import org.junit.Before;
 import org.junit.Test;
@@ -321,6 +323,7 @@ public class AsyncRestTemplateIntegrationTests extends AbstractJettyServerTestCa
 	public void identicalExceptionThroughGetAndCallback() throws Exception {
 		final HttpClientErrorException[] callbackException = new HttpClientErrorException[1];
 
+		final CountDownLatch latch = new CountDownLatch(1);
 		ListenableFuture<?> future = template.execute(baseUrl + "/status/notfound", HttpMethod.GET, null, null);
 		future.addCallback(new ListenableFutureCallback<Object>() {
 			@Override
@@ -328,9 +331,10 @@ public class AsyncRestTemplateIntegrationTests extends AbstractJettyServerTestCa
 				fail("onSuccess not expected");
 			}
 			@Override
-			public void onFailure(Throwable t) {
-				assertTrue(t instanceof HttpClientErrorException);
-				callbackException[0] = (HttpClientErrorException) t;
+			public void onFailure(Throwable ex) {
+				assertTrue(ex instanceof HttpClientErrorException);
+				callbackException[0] = (HttpClientErrorException) ex;
+				latch.countDown();
 			}
 		});
 
@@ -341,6 +345,7 @@ public class AsyncRestTemplateIntegrationTests extends AbstractJettyServerTestCa
 		catch (ExecutionException ex) {
 			Throwable cause = ex.getCause();
 			assertTrue(cause instanceof HttpClientErrorException);
+			latch.await(5, TimeUnit.SECONDS);
 			assertSame(callbackException[0], cause);
 		}
 	}