Fix LinkageError with ExpectedException and FilteredClassPathRunner

Previously, when the ExpectedException JUnit rule was used with
FilteredClassPathRunner a LinkageError would occur if any of
ExpectedException's methods that take a Hamcrest Matcher were called.
This was due to the FilteredClassLoader delegating loading of
org.junit classes to its parent but not org.hamcrest classes. This
resulted in JUnit classes loading one version of the Hamcrest class
and the test class loading another.

This commit ensures that both the JUnit classes and the test class
use the same version of Hamcrest classes by also delegating the
loading of org.hamcrest classes to FilteredClassLoader's parent.

Author: wilkinsona

spring-boot/src/test/java/org/springframework/boot/testutil/FilteredClassPathRunner.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 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.
@@ -264,7 +264,7 @@ private static final class FilteredClassLoader extends URLClassLoader {
 
 		@Override
 		public Class<?> loadClass(String name) throws ClassNotFoundException {
-			if (name.startsWith("org.junit")) {
+			if (name.startsWith("org.junit") || name.startsWith("org.hamcrest")) {
 				return this.junitLoader.loadClass(name);
 			}
 			return super.loadClass(name);

spring-boot/src/test/java/org/springframework/boot/testutil/FilteredClassPathRunnerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 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 +16,13 @@
 
 package org.springframework.boot.testutil;
 
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.ExpectedException;
 import org.junit.runner.RunWith;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.hamcrest.CoreMatchers.isA;
 
 /**
  * Tests for {@link FilteredClassPathRunner}
@@ -33,6 +36,9 @@ public class FilteredClassPathRunnerTests {
 	private static final String EXCLUDED_RESOURCE = "META-INF/services/"
 			+ "javax.validation.spi.ValidationProvider";
 
+	@Rule
+	public ExpectedException thrown = ExpectedException.none();
+
 	@Test
 	public void entriesAreFilteredFromTestClassClassLoader() {
 		assertThat(getClass().getClassLoader().getResource(EXCLUDED_RESOURCE)).isNull();
@@ -44,4 +50,10 @@ public void entriesAreFilteredFromThreadContextClassLoader() {
 				.getResource(EXCLUDED_RESOURCE)).isNull();
 	}
 
+	@Test
+	public void testsThatUseHamcrestWorkCorrectly() {
+		this.thrown.expect(isA(IllegalStateException.class));
+		throw new IllegalStateException();
+	}
+
 }