Avoid race between file creation and its contents being written

Previously, SampleIntegrationParentApplicationTests assumed that when
an output file existed on disk its contents would have been written
in their entirety. This assumption does not hold true and causes the
test to fail intermittently as it incorrectly determines that the test
has produced no output.

This commit updates the test to wait for up to 30 seconds for the
output files to appear on disk and for the expected content to be
found in one of those files. If the files exist but do not
contain the expected content the test will keep trying until it does
or until too much time as elapsed.

Fixes gh-2380

spring-boot-samples/spring-boot-sample-parent-context/src/test/java/sample/parent/consumer/SampleIntegrationParentApplicationTests.java

 /*
- * Copyright 2012-2013 the original author or authors.
+ * Copyright 2012-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,10 +16,7 @@
 
 package sample.parent.consumer;
 
-import java.util.concurrent.Callable;
-import java.util.concurrent.Executors;
-import java.util.concurrent.Future;
-import java.util.concurrent.TimeUnit;
+import java.io.IOException;
 
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
@@ -34,12 +31,13 @@ import org.springframework.util.StreamUtils;
 import sample.parent.SampleParentContextApplication;
 import sample.parent.producer.ProducerApplication;
 
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 /**
  * Basic integration tests for service demo application.
  *
  * @author Dave Syer
+ * @author Andy Wilkinson
  */
 public class SampleIntegrationParentApplicationTests {
 
@@ -60,30 +58,44 @@ public class SampleIntegrationParentApplicationTests {
 	@Test
 	public void testVanillaExchange() throws Exception {
 		SpringApplication.run(ProducerApplication.class, "World");
-		String output = getOutput();
-		assertTrue("Wrong output: " + output, output.contains("Hello World"));
+		awaitOutputContaining("Hello World");
 	}
 
-	private String getOutput() throws Exception {
-		Future<String> future = Executors.newSingleThreadExecutor().submit(
-				new Callable<String>() {
-					@Override
-					public String call() throws Exception {
-						Resource[] resources = new Resource[0];
-						while (resources.length == 0) {
-							Thread.sleep(200);
-							resources = ResourcePatternUtils.getResourcePatternResolver(
-									new DefaultResourceLoader()).getResources(
-									"file:target/output/**");
-						}
-						StringBuilder builder = new StringBuilder();
-						for (Resource resource : resources) {
-							builder.append(new String(StreamUtils
-									.copyToByteArray(resource.getInputStream())));
-						}
-						return builder.toString();
-					}
-				});
-		return future.get(30, TimeUnit.SECONDS);
+	private void awaitOutputContaining(final String requiredContents) throws Exception {
+		long endTime = System.currentTimeMillis() + 30000;
+		String output = null;
+		while (System.currentTimeMillis() < endTime) {
+			Resource[] resources = findResources();
+			if (resources.length == 0) {
+				Thread.sleep(200);
+				resources = findResources();
+			}
+			else {
+				output = readResources(resources);
+				if (output != null && output.contains(requiredContents)) {
+					return;
+				}
+				else {
+					Thread.sleep(200);
+					output = readResources(resources);
+				}
+			}
+		}
+		fail("Timed out awaiting output containing '" + requiredContents
+				+ "'. Output was '" + output + "'");
+	}
+
+	private Resource[] findResources() throws IOException {
+		return ResourcePatternUtils.getResourcePatternResolver(
+				new DefaultResourceLoader()).getResources("file:target/output/**");
+	}
+
+	private String readResources(Resource[] resources) throws IOException {
+		StringBuilder builder = new StringBuilder();
+		for (Resource resource : resources) {
+			builder.append(new String(StreamUtils.copyToByteArray(resource
+					.getInputStream())));
+		}
+		return builder.toString();
 	}
 }