Polish "Fix NPE in BeanDefinitionLoader when XML support is disabled"

See gh-22696

spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/classpath/ModifiedClassPathExtension.java

@@ -41,7 +41,7 @@ import org.springframework.util.ReflectionUtils;
  *
  * @author Christoph Dreis
  */
-class ModifiedClassPathExtension implements InvocationInterceptor {
+public class ModifiedClassPathExtension implements InvocationInterceptor {
 
 	@Override
 	public void interceptBeforeAllMethod(Invocation<Void> invocation,

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/IgnoringXmlBeanDefinitionLoaderTests.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2012-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot;
+
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+import org.springframework.beans.factory.BeanDefinitionStoreException;
+import org.springframework.boot.testsupport.classpath.ModifiedClassPathExtension;
+import org.springframework.context.support.StaticApplicationContext;
+
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+
+@ExtendWith(ModifiedClassPathExtension.class)
+class IgnoringXmlBeanDefinitionLoaderTests {
+
+	@BeforeAll
+	static void ignoreXml() {
+		System.setProperty("spring.xml.ignore", "true");
+	}
+
+	@AfterAll
+	static void enableXml() {
+		System.clearProperty("spring.xml.ignore");
+	}
+
+	@Test
+	void whenXmlSupportIsDisabledXmlSourcesAreRejected() {
+		assertThatExceptionOfType(BeanDefinitionStoreException.class)
+				.isThrownBy(() -> new BeanDefinitionLoader(new StaticApplicationContext(),
+						"classpath:org/springframework/boot/sample-beans.xml").load())
+				.withMessage("Cannot load XML bean definitions when XML support is disabled");
+	}
+
+}